Report on the Radiolaria Collected by H.M.S. Challenger During the Years 1873-1876, First Part: Porulosa (Spumellaria and Acantharia) Report on the Scientific Results of the Voyage of H.M.S. Challenger During the Years 1873-76, Vol. XVIII — Ernst Haeckel

Note: Images of the original pages are available through Internet Archive. See https://archive.org/details/reportonradiolar01haecrich

Project Gutenberg has the other two volumes of this work.
Second Part: Subclass Osculosa; Index
see https://www.gutenberg.org/ebooks/44526.
Plates
see https://www.gutenberg.org/ebooks/44527.

Transcriber's note:

Text enclosed by underscores is in italics (Actissa).

Text enclosed by hash marks is in "gesperrt"
(wide-spaced) type (#Larcoidea#).

Page numbers enclosed by curly braces (example: {25}) have been incorporated to facilitate the use of the Index in Part II.

Some typographical errors in the printed work have been corrected. They are listed at the end of the text.

The Addenda & Errata (Second Part, pp. 1763-4) have been applied without further comment.

REPORT ON THE SCIENTIFIC RESULTS OF THE VOYAGE OF H.M.S. CHALLENGER DURING THE YEARS 1873-76

Under the Command of Captain George S. Nares, R.N., F.R.S. and the Late Captain Frank Tourle Thomson, R.N.

Prepared Under the Superintendence of the Late Sir C. Wyville Thomson, KNT., F.R.S., &c. Regius Professor of Natural History in the University of Edinburgh Director of the Civilian Scientific Staff on Board and Now of John Murray One of the Naturalists of the Expedition

ZOOLOGY--VOL. XVIII.

FIRST PART

Published by Order of Her Majesty's Government

Printed for Her Majesty's Stationary Office
and Sold by
London:--Eyre & Spottiswoode, East Harding Street, Fetter Lane
Edinburgh:--Adam & Charles Black
Dublin:--Hodges, Figgis, & Co.
1887

Price (in Two Parts, with a Volume of Plates) £5, 10s.

CONTENTS.

REPORT on the RADIOLARIA collected by H.M.S. CHALLENGER during the years 1873-1876.

By ERNST HAECKEL, M.D., Ph.D., Professor of Zoology in the University of Jena.

FIRST PART.--PORULOSA.

(#SPUMELLARIA AND ACANTHARIA.#)

EDITORIAL NOTES.

The Report on the RADIOLARIA by Professor Ernst Haeckel of Jena occupies the whole of the present Volume, the text being bound up in Two Separate Parts and the Plates in a Third Part. The Report forms Part XL. of the Zoological Series of Reports on the Scientific Results of the Expedition, and is the largest single Report of the series which has up to this time been published.

The Manuscript of the Systematic Part was written by Professor Haeckel in the English language, and was received by me in instalments on the 12th August 1884, 13th July and 4th December 1885, and 3rd June 1886. The Introduction was written in German and was translated into the English language by Mr. W. E. Hoyle of the Challenger Editorial Staff; the German text being received in instalments between the 15th July 1886, and the 25th January 1887.

The Challenger Naturalists found the representatives of this group of animals to be universally distributed throughout ocean waters, and their dead remains to be nearly equally widely distributed over the floor of the ocean, the relative abundance and the species differing, however, with change of locality, and their abundance or variety being intimately connected with some of the most interesting and intricate problems of general oceanography.

It was a fortunate circumstance that so distinguished a Naturalist, with such an intimate knowledge of the RADIOLARIA, should have been willing to undertake the laborious examination and description of the extensive collections made during the Expedition. Professor Haeckel has devoted ten years of his life to this work, and this Report sets forth the results of his labours, on the conclusion of which he will be congratulated by all Naturalists. The entire literature of the RADIOLARIA (from 1834 to 1884) is completely recorded, and the older species (both living and fossil) redescribed, so that the Report is a complete Monograph, which will be an invaluable aid to all future Investigators.

CHALLENGER OFFICE, 32 QUEEN STREET,
EDINBURGH, 1st February 1887.

THE

VOYAGE OF H.M.S. CHALLENGER.

#ZOOLOGY.#

Report on the RADIOLARIA collected by H.M.S. Challenger during the Years 1873-76. By ERNST HAECKEL, M.D., Ph.D., Professor of Zoology in the University of Jena.

PREFACE.

The significance of the Radiolaria in regard to the relations of life in the ocean has been increased in a most unexpected manner by the discoveries of the Challenger. Large swarms of these delicate Rhizopoda were found not only at the surface of the open ocean but also in its different bathymetrical zones. Thousands of new species make up the wonderful Radiolarian ooze, which covers large areas of the deep-sea bed, and was brought up from abysses of from 2000 to 4000 fathoms by the sounding machine of the Challenger. They open a new world to morphological investigation.

When ten years ago (in the autumn of 1876) I accepted the enticing invitation of Sir Wyville Thomson to undertake the investigation of these microscopic creatures, I hoped to be able to accomplish the task with some degree of completeness within a period of from three to five years, but the further my investigations proceeded the more immeasurable seemed the range of forms, like the boundless firmament of stars. I soon found myself compelled to decide between making a detailed study of a selection of special forms or giving as complete a survey as possible of the varied forms of the whole class; and I decided upon the latter course, having regard both to the general plan of the Challenger Reports, and to the interests of our acquaintance with the class as a whole. I must, however, confess at the close of my work that my original intention is far from having been fulfilled. The extraordinary extent and varied difficulties of the undertaking must excuse the many deficiencies.

The special examination of the Challenger collection was for the most part completed in the summer of 1881; I collected its results in my Entwurf eines Radiolarien-Systems auf Grund von Studien der Challenger-Radiolarien (Jenaische Zeitschr. f. Naturw., Bd. xv., 1881). Since the manuscript of this preliminary communication was completed only a few days before my departure for Ceylon, and since I was unable to correct the proofs myself, several errors have crept into the Prodromus Systematis Radiolarium included in it. These have been corrected in the following more extensive working out of it. Even at that time I had distinguished 630 genera and more than 2000 species; but on the revision of these, which I undertook immediately on my return from India, this number was considerably increased. The total number of forms here described amounts to 739 genera and 4318 species; of these 3508 are new, as against 810 previously described. In spite of this large number, however, and in spite of the astonishing variety of the new and marvellous forms, the riches of the Challenger collection are by no means exhausted. A careful and patient worker who would devote a second decade to the work, would probably increase the number of new forms (especially of the smaller ones) by more than a thousand; but for a really complete examination, the lifetime of one man would not suffice.

The richest source of the Challenger material is the Radiolarian ooze of the central Pacific Ocean (Stations 265 to 274). This remarkable deep-sea mud consists for the greater part of well-preserved siliceous shells of Polycystina (SPUMELLARIA and NASSELLARIA). Not less important, however, especially for the study of the ACANTHARIA and PHÆODARIA, are the wonderful preparations stained with carmine and mounted in Canada balsam on the spot by Dr. John Murray. One such preparation (e.g., from Station 271) often contains twenty or thirty, sometimes even fifty new species. In many of these preparations the individual parts of the unicellular organism are so well preserved that they show clearly the characteristic peculiarities of the legions and orders. Since the material for these preparations was taken with the tow-net, not only from the surface of the sea but also from different bathymetrical zones, it furnishes valuable conclusions regarding the chorology, as well as the physiology and morphology of the group. For many new discoveries I am indebted to the study of such preparations, of which I have examined about a thousand from 168 different Stations (compare § 240). In addition to these about 100 bottles were handed to me, containing partly bottom-deposits, partly tow-net gatherings.

Sir Wyville Thomson, who directed the investigations of the Challenger with so much devotion, and only partly saw its results, has laid me under a deep debt of obligation; not less is this the case, however, with his successor, Dr. John Murray. I am especially indebted to both gentlemen for the freedom they have allowed me in the carrying out of my work, and especially for the permission to include a description of all known Radiolaria in the Challenger Report, which has thus become a second edition many times enlarged of my Monograph published in 1862. Since all previous literature of the subject has been consulted and critically revised, it is hoped that this Report will form a useful foundation for future investigations. All names of sufficiently described Radiolaria published during the first half century of our knowledge of the class (from 1834 to 1884), are inserted in alphabetical order in the index at the end of this work.

In addition to the treasures of the Challenger, my own collection of Radiolaria has yielded many new forms whose description is here included. On my journeys to the Mediterranean (an account of which is given in the introduction to my Monograph of the Medusæ), I have given special attention to these delicate microscopic organisms for more than thirty years. Besides the various points on the Mediterranean, the Atlantic Ocean at the Canaries (in the winter of 1866-67) yielded many interesting new forms; whilst my voyage across the Indian Ocean, from Aden to Bombay, in November 1881, thence to Ceylon and back by Socotra in March 1882, was still more productive. In particular, some extended excursions which I had the opportunity of making from Belligemma and Matura (at the southern extremity of Ceylon) gave me an insight into the rich treasures of the Indian Ocean.

Most important, however, as regards the knowledge of the Indian Radiolaria, are the collections which Captain Heinrich Rabbe of Bremen has so beautifully preserved during his many voyages through that region. In the neighbourhood of Madagascar and the Cocos Islands more especially, and also in the Sunda Archipelago, he met with large swarms of Radiolaria, among which were many new and remarkable forms. These were of special value for completing the chorology, and the more so since the course of the Challenger in the Indian Ocean lay very far to the southwards. I will therefore take this opportunity of repeating my best thanks to Captain Rabbe for the friendly donation of his valuable collection.

The Radiolarian fauna of the North Atlantic Ocean, which was previously but little known and only slightly increased by the investigations of the Challenger, received a valuable increase from the interesting collections made by Dr. John Murray on various expeditions to the Færöe Islands (on the "Knight Errant" in 1880 and on the "Triton" in 1882). A large number of new Radiolaria were captured in the Færöe Channel, partly at the surface of the Gulf Stream, partly at various depths, and the proof was thus furnished that at certain points in the North Atlantic Ocean Radiolaria are very richly developed. I am further indebted to Dr. John Murray for the free use of this important material as well as for much other assistance in the carrying out of my work. Another rich source of Radiolaria I found in the alimentary canal of pelagic animals from all seas. Medusæ, Siphonophoræ, Salpæ, Pteropoda, Heteropoda, Crustacea, &c., which live partly at the surface of the sea and partly at various depths, and swallow large masses of Radiolaria, often contain numbers of their shells well-preserved in their intestine. The alimentary canal of Fishes and Cephalopods too, which live upon these pelagic animal frequently contains considerable quantities of siliceous shells; and another newly discovered source has been found in the coprolites of the Jurassic period, which consist largely of Radiolarian skeletons.

In the investigation of this complicated system of organisms, I have endeavoured on the one hand to give accurately the forms and dimensions of the species observed, and on the other hand to present a survey of the relationships of the different genera and families; and in this I have striven especially to combine the phylogenetic aims of the natural system with the essentially artificial divisions of a practical classification. Being, however, a conscientious supporter of the theory of descent, I can of course lay no stress upon the value of the categories, which are here distinguished as Legions, Orders, Families, Genera, &c. All these artificial systematic grades I regard as of merely relative value; and from the same cause I attach no importance to the distinction of all the species here described; many of them are probably only developmental stages, and like my predecessors I have determined their boundaries on subjective grounds. In the systematic working out of so much material one always runs the risk of doing either too much or too little in the way of creating species; but in the light of the theory of descent this danger is of no consequence.

In the carrying out of this extensive task the friendly aid of Dr. Reinhold Teuscher of Jena was of the greatest benefit to me; at my request he was at the trouble of making a large number of accurate drawings with the camera lucida, and he also undertook a long series, amounting to some 8000, accurate micrometric measurements, which were of the greatest value in the attempt to settle the important question of the constancy of the various species; I have alluded to this in a note at the conclusion of the Report (p. 1760). My best thanks are due to Dr. Teuscher for the patient and careful manner in which he discharged these tedious tasks.

The figures of new species of Radiolaria (about 1600 in number) which appear in the atlas of one hundred and forty plates accompanying this Report, were nearly all drawn with the camera lucida, partly by Mr. Adolph Giltsch and partly by myself. The names of the genera which appear at the bottom of the plates have in many cases been changed since they were printed off, as may be seen from the explanations which accompany them. Had it been possible to complete the examination of the material before the plates were commenced this might have been avoided, and in many cases a better selection of figures might have been made. All the drawings have been made upon the stone by the practised hand of Mr. Adolph Giltsch, in his usual masterly manner, and his lithographic work, which has lasted fully ten years, is the more valuable since he has himself microscopically studied the greater part of the species figured. The fact that the atlas presents so full a picture of the marvellous wealth of form of the Radiolaria is especially due to his lively interest in the work, to his unwearying care, and to his morphological acuteness. May it be the means of inducing many naturalists to study more deeply this inexhaustible kingdom of microscopic life, whose endless variety of wonderful forms justifies the saying--Natura in minimis maxima.

CONTENTS.

FIRST PART.

GENERAL INTRODUCTION-- PAGE

I. Anatomical Section (§§ 1-140), i Chapter I. The Unicellular Organism, i " II. The Central Capsule, xxiv " III. The Extracapsulum, li " IV. The Skeleton, lxviii

II. Biogenetical Section (§§ 141-200), xciii Chapter V. Ontogeny (Individual Development), xciii " VI. Phylogeny (Genealogical Development), ci

III. Physiological Section (§§ 201-225), cxxviii Chapter VII. Vegetative Functions, cxxviii " VIII. Animal Functions, cxl

IV. Chorological Section (§§ 226-250), cxlvi Chapter IX. Geographical Distribution, cxlvi " X. Geological Distribution, clxiv

V. Bibliographical Section (§§ 251-254), clxxvi

SYSTEMATIC PART, 1

I. Subclass PORULOSA, 6 Legion I. SPUMELLARIA vel PERIPYLEA, 6 Order 1. Colloidea, 10 " 2. Beloidea, 28 " 3. Sphæroidea, 50 " 4. Prunoidea, 284 " 5. Discoidea, 402 " 6. Larcoidea, 599

Legion II. ACANTHARIA vel ACTIPYLEA, 716 Order 7. Actinelida, 728 " 8. Acanthonida, 740 " 9. Sphærophracta, 795 " 10. Prunophracta, 859

SECOND PART.

II. Subclass OSCULOSA, 889 Legion III. NASSELLARIA vel MONOPYLEA, 889 Order 11. Nassoidea, 895 " 12. Plectoidea, 898 " 13. Stephoidea, 931 " 14. Spyroidea, 1015 " 15. Botryodea, 1103 " 16. Cyrtoidea, 1126

Legion IV. PHÆODARIA vel CANNOPYLEA, 1521 Order 17. Phæocystina, 1542 " 18. Phæosphæria, 1590 " 19. Phæogromia, 1642 " 20. Phæoconchia, 1710

Note on the Dimensions and Measurements, 1760

ADDENDA, 1761

ERRATA, 1763

INDEX, 1765

GENERAL INTRODUCTION.

----

ANATOMICAL SECTION.

A SKETCH OF OUR KNOWLEDGE OF THE ORGANISATION OF THE RADIOLARIA IN THE YEAR 1884.

----

CHAPTER I.--THE UNICELLULAR ORGANISM.

(§§ 1-50.)

1. Definition of the Radiolaria.--RADIOLARIA are marine Rhizopoda, whose unicellular body always consists of two main portions, separated by a membrane; an inner Central capsule (with one or more nuclei) and an Extracapsulum (the external calymma, which has no nucleus, and the pseudopodia); the endoplasm of the former and the exoplasm of the latter are connected by openings in the capsule-membrane. The central capsule is partly the general central organ of the Radiolarian cell, partly the special organ of reproduction, since its intracapsular protoplasm, along with the nuclei embedded in it, serves for the formation of flagellate spores. The extracapsulum is partly the general organ for intercourse with the outer world (by means of the pseudopodia), partly the special organ of protection (calymma) and nutrition (sarcomatrix). The majority of Radiolaria develop also a skeleton for support and protection, which presents the utmost variety of form, and is generally composed of silica, sometimes of an organic substance (acanthin). The Radiolarian cell usually leads an isolated existence (Monozoa vel Monocyttaria); only in a small minority (of one legion) are the unicellular organisms united in colonies or coenobia (Polyzoa vel Polycyttaria).

The extent of the Radiolaria, as limited by the above definition, which I have made as compact as possible, differs in several important respects from that allowed to the group by all previous diagnoses. The shortest expression of its scope might perhaps be:--Rhizopoda with central capsule and calymma; for the most important character of the Radiolaria, and that by which they are distinguished from all other Rhizopoda, is the differentiation of the unicellular body into two principal parts of equal importance and their separation by a constant capsule-membrane.

2. The Two Subclasses of the Radiolaria.--The systematic catalogue of the Radiolaria, which forms the second part of this Report, and is brought up to the year {ii}1884, contains 20 orders, 85 families, 739 genera, and 4318 species. The consideration that but a small proportion of the ocean his yet been investigated renders it likely, however, that even this large number does not include the half of the recent species. The great progress which our knowledge of the organisation of the Radiolaria has made, by means of comparative study, renders it possible to arrange this enormous mass of forms in four main divisions or legions, and these are again related in pairs, so that two divisions of the highest rank or subclasses are constituted, the Porulosa (or Holotrypasta) and Osculosa (or Merotrypasta).

The division of the Radiolaria into two subclasses and four legions (or principal orders), I sought to establish in 1883 in a communication on the Orders of the Radiolaria (Sitzb. Jena Gesellsch. Med. u. Naturwiss., February 16, 1883). As a believer in the theory of descent, I regard all the systematic arrangements of specialists as artificial, and all their divisions as subjective abstractions, and hence I shall be guided in the establishment of such groups as subclasses, legions, orders, &c., by purely practical considerations, especially by the desire to give as ready a survey as possible of the complex multitude of forms (compare §§ 154 to 156).

3. Porulosa or Holotrypasta.--The subclass Porulosa or Holotrypasta includes the two legions, PERIPYLEA or SPUMELLARIA, and ACTIPYLEA or ACANTHARIA, which agree in the following constant and important characters:--(1) The Central Capsule is primitively a sphere, and retains this homaxon form in the majority of the species. (2) The Membrane of the central capsule is everywhere perforated by very numerous minute pores, but possesses no larger principal aperture (osculum). (3) The Pseudopodia radiate in all directions and in great numbers from the central capsule, passing through its pores. (4) The Equilibrium of the floating unicellular body is in most Porulosa pantostatic (indifferent) or polystatic (plural-stable), since a vertical axis is either absent, or, if present, has its two poles similarly constituted. (5) The Ground-forms of the skeleton are therefore almost always either spherotypic or isopolar-monaxon, very rarely zygotypic. The two legions of the Porulosa are distinguished mainly by the skeleton of the SPUMELLARIA (or PERIPYLEA) being siliceous, never centrogenous, nor composed of acanthin, whilst in the ACANTHARIA (or ACTIPYLEA) it is always centrogenous and made up of acanthin; hence in the former the nucleus is always central, in the latter always excentric.

4. Osculosa or Merotrypasta.--The subclass Osculosa or Merotrypasta includes the two legions MONOPYLEA or NASSELLARIA, and CANNOPYLEA or PHÆODARIA, which agree in the following constant and important characters:--(1) The Central Capsule is originally monaxon (ovoid or spheroidal) and retains this ground-form in most of the species. (2) The Membrane of the central capsule possesses a single large principal aperture (osculum) at the basal pole of the vertical main axis. (3) The Pseudopodia radiate from a stream of sarcode which passes out from the central capsule only on one side, namely, through the principal aperture. (4) The Equilibrium of the floating body is {iii}monostatic or unistable, since the two poles of the principal axis are always more or less different from each other. (5) The Ground-forms of the skeleton are, therefore, for the most part grammotypic (centraxon) or zygotypic (centroplan), rarely spherotypic. The two legions of the Osculosa are distinguished chiefly by the principal opening (osculum) being closed by a porous plate (porochora with its podoconus) in the NASSELLARIA (or MONOPYLEA), and by a radiate cover (operculum with its astropyle) in the PHÆODARIA (or CANNOPYLEA).

5. The four Legions of Radiolaria.--The four principal groups of Radiolaria, to which we have given the name "legions," are natural units, since the most important peculiarities in the structure of the central capsule are quite constant within the limits of the same legion, and since all the forms in the same legion may be traced without violence to the same phylogenetic stem. The four legions are, however, related to each other, in so far as they all exhibit those characters which distinguish the Radiolaria from other Protista. The two which compose the Porulosa (§ 3) seem somewhat more nearly related to each other than to the two which make up the Osculosa (§ 4). When, however, the attempt is made to bring them all into a phylogenetic relationship, it undoubtedly appears that the SPUMELLARIA (or PERIPYLEA) are the primitive stem, out of which the other three have been developed as independent branches. All three have been derived, probably independently, from the most ancient stem-form of the SPUMELLARIA, the spherical Actissa.

6. Peripylea or Spumellaria.--Those Radiolaria which we call "PERIPYLEA" on account of the constitution of their central capsule, or "SPUMELLARIA" on account of the nature of their skeleton, are separated from the other three legions of the class by the combination of the following constant characters:--(1) The Membrane of the central capsule is single and evenly perforated all over by innumerable fine pore-canals, but without any larger principal opening (osculum). (2) The Nucleus always lies centrally in the SPUMELLARIA monozoa and is serotinous, for it divides only at a later period into the nuclei of the spores; in the SPUMELLARIA polyzoa it is precocious, and divides early into many small nuclei. (3) The Pseudopodia are exceedingly numerous and distributed evenly over the whole surface of the central capsule. (4) The Calymma contains no phæodium. (5) The Skeleton is seldom wanting, is never centrogenous, and is always siliceous. (6) The Ground-form of the central capsule is originally spherical (often modified); that of the skeleton is also spherical or, in the majority of cases, derived in different ways from the sphere.

7. Actipylea or Acantharia.--These Radiolaria which we call "ACTIPYLEA" on account of the constitution of their central capsule, or "ACANTHARIA" from the formation of their skeleton, are separated from the other three legions by the combination of the following constant characters:--(1) The Membrane of the central capsule is single and {iv}perforated by numerous fine pore-canals, which are regularly distributed in series or groups, but without a larger principal opening (osculum). (2) The Nucleus is always excentric and generally precocious, since it divides early by a peculiar process of budding into numerous small nuclei. (3) The Pseudopodia are very numerous and distributed regularly in groups (or series united into a network). (4) The Calymma contains no phæodium. (5) The Skeleton is generally present, always centrogenous, and composed of acanthin. (6) The Ground-form of the central capsule is originally spherical (often modified), that of the skeleton polyaxon (often modified).

8. Monopylea or Nassellaria.--Those Radiolaria which we call "MONOPYLEA" from the formation of their central capsule, or "NASSELLARIA" from the nature of their skeleton, are distinguished from the other three legions of the class by the combination of the following constant characters:--(1) The Membrane of the central capsule is single, and has only one large principal opening (osculum) at the basal pole of the vertical main axis; this osculum is closed by a perforated lid (porochora or operculum porosum) from which there arises within the central capsule a peculiar cone of threads or pseudopodia (podoconus). (2) The Nucleus is usually excentric and is always serotinous, since it only divides at a comparatively late period into spore-nuclei. (3) The Pseudopodia are not very numerous and arise by division of a single stem or bundle of threads of sarcode, which issues from the porochora. (4) The Calymma contains no phæodium. (5) The Skeleton (very rarely absent) is never centrogenous, but always extracapsular and siliceous. (6) The Ground-form of the central capsule is always monaxon (with a vertical allopolar main axis), originally ovoid, often modified; that of the skeleton is also generally monaxon, often modified (triradial or bilateral).

9. Cannopylea or Phæodaria.--Those Radiolaria which we call "CANNOPYLEA" from the constitution of their central capsule, or "PHÆODARIA" on account of their peculiar phæodium, are distinguished from the other three legions by the combination of the following characters:--(1) The Membrane of the central capsule is double, consisting of a strong outer and delicate inner capsule, and has only one principal opening (osculum) at the basal pole of the vertical main axis; this osculum is closed by a radiate cover (astropyle or operculum radiatum), from the centre of which arises an external tubular spout (proboscis). Occasionally a few small accessory openings (parapylæ) are present besides the principal opening. (2) The Nucleus lies centrally or subcentrally in the capsule (in the vertical main axis), and is serotinous, inasmuch as it only divides at a late period into spore-nuclei. (3) The Pseudopodia are usually very numerous and arise from a thick sarcomatrix, formed by the spreading out of a thick stem of sarcode, which issues from the astropyle. (4) The Calymma always contains a phæodium or peculiar voluminous excentric mass of pigment. (5) The Skeleton (very rarely absent) is never centrogenous, always extracapsular and formed of a silicate of carbon. (6) The {v}_Ground-form_ of the central capsule is always monaxon (with a vertical allopolar main axis) and generally spheroidal; that of the skeleton is very varied.

10. Synopsis of the Subclasses and Legions:--

11. Individuality of the Radiolaria.--Like other Protozoa the Radiolaria are unicellular organisms, the whole fully developed organisation of which falls under the category of a single cell, both morphologically and physiologically. Since this view is based upon the composition of the individual body out of two different morphological elements, nucleus and protoplasm, it is at once justified in the case of the majority of Radiolaria, in which the plasmatic body encloses only a single nucleus (the so-called "Binnen-Bläschen"); such is the case in all the SPUMELLARIA monozoa, NASSELLARIA and PHÆODARIA. This aspect of the case might appear doubtful in those Radiolaria in which the simple primary cell-nucleus divides early into numerous small secondary nuclei, as is the case in the SPUMELLARIA polyzoa and most ACANTHARIA. Strictly speaking, the multinucleate central capsule should in such cases be regarded as a syncytium; but since the individual unity of the unicellular organism is as clearly defined in these precocious multinuclear Radiolaria as in the ordinary serotinous forms, the former must be considered unicellular Rhizopods just as are the latter. This mode of regarding {vi}the case is the more necessary, inasmuch as the early division of the nucleus has no further influence upon the organisation. Just as in many other classes of the Protista there are monozootic (solitary) and polyzootic (social) forms, so also in the Radiolaria there are in addition to the ordinary monozootic or monobious forms certain families in which colonies or coenobia are formed by the association of individuals; this distinction may be expressed by the terms "Monocyttaria" and "Polycyttaria."

The unicellular nature of the Radiolaria was first established by Richard Hertwig in 1879 (L. N. 33),[1] and brought into conformity with our present histiological knowledge and the new reform of the cell-theory. Huxley, however, who was in 1851 the first to examine living Radiolaria accurately, declared Thalassicolla nucleata to be a unicellular Protozoon, and the individual central capsules of Sphærozoum punctatum to be cells, but, owing to the then condition of the cell-theory, he was unable to give a conclusive demonstration of this view. Later, when Johannes Müller in 1858 and myself in 1862 recognised the peculiar "yellow cells" which occur in large numbers in many Radiolaria as true nucleated cells, it appeared impossible any longer to maintain the unicellular nature of the Radiolaria; also the great complication which I showed to exist in the structure of Thalassicolla appeared to contradict it. Only after Cienkowski (1871) and Brandt (1881) had shown that the "yellow cells" do not belong to the Radiolarian organism, but are symbiotic unicellular algæ, was it possible to revive and demonstrate anew the unicellular nature of the Radiolaria.

12. Morphological Individuality.--From the morphological standpoint the individuality of the unicellular elementary organism is obvious in the ordinary solitary Radiolaria (Monobia), and is to be so regarded that the whole body with all its constituent parts, and not merely the central capsule, is to be regarded as a cell. Naturally the xanthellæ or yellow cells (§§ 76, 90), which as independent algæ live in symbiosis with many Radiolaria, must be excluded. The unicellular organisation of the Radiolaria is further to be distinguished from that of the other Protista, inasmuch as an internal membrane (capsule-membrane) separates the central (medullary) from the peripheral (cortical) portion. In the coenobia of the social Radiolaria (or Polycyttaria), the morphological individuality persists only as regards the medullary portions of the aggregated cells (the individual central capsules), while the cortical portions fuse completely to form a common extracapsulum. Hence in these SPUMELLARIA polyzoa two different stages of morphological individuality must be distinguished, the Cell as a Morphon of the first stage, and the Coenobium as a Morphon of the second stage.

13. Physiological Individuality.--From the physiological standpoint also the individuality of the unicellular organism is immediately obvious in the case of the ordinary solitary Radiolaria (Monobia); as in other Protista it fulfils all the functions of life by itself alone. This physiological individuality of the monobious Radiolarian cell is furthermore not influenced by the xanthellæ, which live as independent algæ in symbiosis with many Radiolaria; even though these often by the production of starch assist in the {vii}nourishment of the Radiolaria, yet they are by no means indispensable to them. On the other hand, the physiological individuality offers more complicated relations in the social Radiolaria (Polycyttaria) which live united in colonies or coenobia. Here the actual Bion (or the fully developed physiological individual) is not represented by the individual cells, but by the whole multicellular coenobium, which in each species has a definite form and size. In these coenobia, which are usually spherical or cylindrical jelly-like masses, several millimeters in diameter, numerous cells are so intimately united that only their medullary portions (the central capsule with the endoplasm) remain independent; the cortical portions (calymma and exoplasm) on the contrary uniting into a common extracapsulum. This discharges, as a whole, the functions of locomotion, sensation, and inception of nutriment, while the separate central capsules act in the main only as reproductive organs (forming spores) and partly also as the central organs of metastasis (digestion). Each coenobium may also be regarded as a polycyttarium, i.e., a "multicellular Radiolarian," whose numerous central capsules represent so many sporangia or spore-capsules.

On this head compare the section in my monograph of 1862 (L. N. 16), entitled Die Organisation der Radiolarien-Colonien; Polyzoen oder Polycyttarien? (pp. 116 to 126); and also R. Hertwig, Zur Histologie der Radiolarien, 1876 (L. N. 26, p. 23).

14. Monocyttaria and Polycyttaria.--In the majority of the Radiolaria each unicellular organism passes its individual life in an isolated condition (as a Monocyttarium). Only in a part of the SPUMELLARIA numerous unicellular individuals are united into societies which are regarded as coenobia or colonies (Polycyttaria). This is the case in three different families belonging to the PERIPYLEA, in the Collozoida (without a skeleton, Pl. 3), the Sphærozoida (with a Beloid skeleton, Pl. 4), and the Collosphærida (with a Sphæroid skeleton, Pls. 5-8). All three families of Polycyttaria (or social Radiolaria), agree in their mode of forming colonies, since the central capsules of the social individuals remain separate and lie in a common jelly-like mass, which is formed by the fusion of their extracapsulum. The chief part of the voluminous colonies, which attain a diameter of several millimetres (sometimes more than 1 cm.), and are generally spherical, ellipsoidal or cylindrical, consists therefore of the jelly-like calymma, and this is penetrated by a sarcoplegma, to whose meshes all the individual organisms contribute by means of the pseudopodia, which radiate from their sarcomatrix. A further peculiarity in which the social SPUMELLARIA differ from the solitary consists in the fact that the former are precocious and the latter serotinous in the division of the nucleus (§ 64). Whilst in the solitary or monozootic SPUMELLARIA the middle of the central capsule is occupied by the simple nucleus, and this divides only at a late period (immediately before the formation of spores) into the numerous spore nuclei, in the colonial or polyzootic SPUMELLARIA this division takes place very early, and the middle of each central capsule is usually occupied by an oil-globule.

{viii}The colonial Radiolaria were described as early as the year 1834 by Meyen, the first investigator of the class, under the name Sphærozoum, and, as Palmellaria, compared with the gelatinous colonies of the Nostochineæ. The first accurate observations upon their structure were, however, made in 1851 by Huxley, who described examples of all three families under the name Thalassicolla punctata. More extended, however, were the investigations of Johannes Müller, who in his fundamental work (1858) divided the whole class Radiolaria into Solitaria and Polyzoa. The Radiolaria solitaria he divided into Thalassicolla, Polycystina and Acanthometra, the Radiolaria polyzoa into Sphærozoa (without a shell) and Collosphæra (with a shell). The most accurate delineation of the Polycyttaria was given by Hertwig in his beautiful memoir, Zur Histologie der Radiolarien (1876). Quite recently, however (1886), since the completion of my manuscript upon the Challenger Radiolaria, a very complete Monograph of the Polycyttaria has appeared by Karl Brandt, Die colonie-bildenden Radiolarien (Sphærozoen) des Golfes von Neapel und der angrenzenden Meeres-Abschnitte (276 pp., 8 pls., Berlin). It contains in particular most valuable contributions to the physiology and histology.

15. The Central Capsule and Extracapsulum.--The special peculiarity of the unicellular Radiolarian organism, by which it is clearly distinguished from all other Rhizopoda (and indeed from most other Protista), is its differentiation into two separate chief constituents, the central capsule and extracapsulum, and the formation of a special membrane which separates them. This, the capsule-membrane, is not to be compared with an ordinary cell-membrane, as an external layer, but rather to be regarded as an internal differentiated product. The extracapsulum or external (cortical) portion of the body is in most Radiolaria more voluminous than the central capsule or inner (medullary) portion. The exoplasm of the former (the cortical or extracapsular protoplasm) is emphatically different from the endoplasm of the latter (the medullary or intracapsular protoplasm). Besides the most important vital processes are distributed by division of labour so completely between them that they appear most distinctly co-ordinated. The central capsule is on the one hand the general central organ of the "cell-soul" for the discharge of its sensory and motor functions (comparable to a ganglion-cell), on the other hand the special organ of reproduction (sporangium). The extracapsulum, also, is not less significant, since on the one hand its calymma acts as a protecting envelope to the central capsule, as a support to the pseudopodia, and a foundation for the skeleton or a matrix for the development of the shell, and on the other hand its pseudopodia are of the utmost importance as peripheral organs of movement and sensation as well as of nutrition and respiration. The central capsule and the extracapsulum are therefore to be regarded both morphologically and physiologically as the two characteristic co-ordinated principal parts of the unicellular Radiolarian organism.

In most of the more modern delineations of the Radiolaria the central capsule is regarded as the "cell proper" and its membrane as the "cell-wall." The following facts are opposed to the correctness of this interpretation:--1. In most Radiolaria the exoplasm is clearly different from {ix}the endoplasm, and the former is more voluminous than the latter. 2. In all Radiolaria the division of labour is so carried out between the central capsule and the extracapsulum, that the physiological significance and independence of both principal parts of the cell is almost equally great. 3. It is only in the ACANTHARIA that the formation of the skeleton takes place within the central capsule; in all the other three legions it is quite independent of it.

16. The Malacoma and Skeleton.--Whilst the division of the unicellular organism into central capsule and extracapsulum is undoubtedly the most important character of the Radiolarian organism, the development of a skeleton of peculiar and most varied form is of very striking significance. This skeleton is always a secondary product of the cell, but is always anatomically so independent, and so clearly marked off from the soft parts or malacoma, that it seems advisable to regard both separately in a general morphological survey. The skeleton stands in a different relation to each of the two principal constituents of the malacoma. Only in the ACANTHARIA is it centrogenous and developed from the central capsule outwards. In the other three legions the skeleton never arises in the centre of the capsule; in the NASSELLARIA and PHÆODARIA it is always extracapsular; in the SPUMELLARIA it is also outside the central capsule originally, but afterwards becomes often surrounded by it, and finally lies in most cases partly within and partly without the central capsule. The chemical basis of the skeleton in the ACANTHARIA is the curious acanthin (an organic substance allied to chitin), in the PHÆODARIA a silicate of carbon, and in the NASSELLARIA and SPUMELLARIA silica.

17. Ground-Forms of the Radiolaria (Promorphology).--The ground-forms of the Radiolaria exhibit a greater variety than those of any other class in the organic world, greater indeed than is to be found in all the remaining groups together. For every conceivable ground-form which can be defined in the system of promorphology is actually present in the Radiolaria; their skeleton exhibits, as it were, in material existence, certain geometrical ground-forms which are found in no other organisms. The cause of this unexampled richness in different forms lies chiefly in the static relations of the Radiolaria, which swim freely in the sea, partly also in the peculiar plasticity of their protoplasm and the material of their skeletons.

Regarding the general system of ground-forms compare my Generelle Morphologie (1866, Bd. i. pp. 375-552; Bd. iv., Allgemeine Grundformenlehre). The ground-forms there proposed and systematically defined have, however, found but little acceptance (chiefly, no doubt, owing to the difficult and complicated nomenclature); but having now, twenty years after their publication, anew carefully revised and critically studied them, I can find no sufficient reason for abandoning the principles there adopted. On the contrary the study of the Challenger Radiolaria during the last ten years, with its incomparable wealth of forms, has only confirmed the accuracy of my system of ground-forms. The customary treatment of these in zoological and botanical handbooks (such as those of Claus and Sachs) is quite insufficient.

{x}18. The Principal Groups of Geometrical Ground-Forms.--The great variety of the geometrical ground-forms which are actually realised in the variously shaped bodies of the Radiolaria, renders it desirable to classify these in as small a number as possible of principal groups and a larger number of subdivisions. As extensive principal groups four at least must be distinguished; the Centrostigma or Sphærotypic, the Centraxonia or Grammotypic, the Centroplana or Zygotypic, and the Acentrica or Atypic. The natural centre of the body, about which all its parts are regularly arranged, is in the first group a point (stigma), in the second a straight line (principal axis), in the third a plane (sagittal plane), in the fourth a centre is of course wanting.

19. The Centrostigma or Sphærotypic Ground-Forms.--The first group of geometrical ground-forms, here distinguished as sphærotypic or the centrostigma, is undoubtedly the most important among the Radiolaria, inasmuch as if these be considered monophyletic, it must be the original one from which all the other ground-forms have been derived. The common character of all these sphærotypic ground-forms is that their natural centre is a point (stigma); thus there is no single principal axis (or protaxon) such as is characteristic of the two following groups. The sphærotypic ground-forms are subdivided into two important smaller groups, the spheres (Homaxonia) and the endospherical polyhedra (Polyaxonia). The spherical ground-forms, fully developed in the central capsule and calymma of Actissa and the #Sphæroidea# as well as in many ACANTHARIA, present no different axes; all possible axes passing through the centre of the body are equal (Homaxonia). In the endospherical polyhedra, on the contrary, numerous axes (three at least) may be distinguished, which are precisely equal to each other and different from all the remaining axes (Polyaxonia). If the extremities of these axes, or the poles, which are all equidistant from the common centre, be united by straight lines, a polyhedral figure is produced whose angles all lie in the surface of the sphere. According as the poles of the axes are at equal, subequal, or at different distances from each other, we may divide the endospherical polyhedra into regular, subregular and irregular. (See Gener. Morphol., Bd. i. pp. 404-416.)

20. The Centraxonia or Grammotypic Ground-Forms.--The second principal group of organic ground-forms, here called grammotypic or centraxonia, is characterised by the fact that a straight line (gramma) or a single principal axis (protaxon) forms the natural centre of the body. This important and extensive group is divided into two subgroups, those with one axis (Monaxonia) and those with crossed axes (Stauraxonia); in the latter different secondary transverse or cross-axes may be distinguished, but not in the former. In the Monaxonia, therefore, every transverse section of the body perpendicular to the principal axis is a circle, in the Stauraxonia, on the contrary, a polygon. The Monaxonia are further subdivided into two groups, in one of which the two poles of the principal axis {xi}are equal and similar (Isopolar), in the other of which they are different (Allopolar); in the former the two halves of the body, which are separated by the equatorial plane (or the largest transverse plane, perpendicular to the principal axis), are equal, in the latter unequal. Among the isopolar uniaxial ground-forms (Monaxonia isopola) may be mentioned the ellipsoidal, spheroidal, lenticular, &c.; to the allopolar uniaxial forms (Monaxonia allopola) belong the conical, hemispherical, ovoid, &c. In the same way the pyramidal ground-forms with crossed axes are divisible into two groups, according as the two poles of the principal axis are equal or not. The ground-form of the former is the double pyramid, that of the latter the single pyramid. Both the double and the single pyramids may again be subdivided, each into two important lesser groups, the regular and the amphithect. In the first division the equatorial plane of the double and the basal plane of the single pyramid is a regular polygon (square, &c.), whilst in the other division it is an elongated or amphithect polygon (rhombus, &c.); the crossed axes are equal in the former, unequal in the latter. (See Gener. Morphol., Bd. i. pp. 416-494.)

21. The Centroplana or Zygotypic Ground-Forms.--The third principal group of ground-forms includes those which are bilaterally symmetrical in the ordinary sense, or zeugitic or zygotypic; the natural centre of their body is a plane. These forms are the only ones in which the distinction between right and left is possible, since their body is divided by the median plane (planum sagittale) into two symmetrical halves (right and left). In all these zeugites the position of every part is determined by three axes perpendicular to each other, and of these three dimensive axes two are allopolar, one is isopolar. The two unlike poles of the principal (or longitudinal) axis are the oral and aboral, the two unlike poles of the sagittal (or vertical) axis are the dorsal and ventral; the two similar poles of the frontal (or transverse) axis, however, are the right and left. This important group of zeugitic or bilateral forms may also be divided into two clearly distinct lesser groups, the Amphipleura and the Zygopleura. In the Amphipleura (or bilaterally radial ground-forms) the "radial two-sided" body is produced by modification of a regular pyramid (as Spatangus from Echinus), and hence is composed of several (not less than three) antimeres. In the Zygopleura (or bilaterally symmetrical ground-forms) on the other hand, the bodies consist of two antimeres (as in all the higher animals, Vertebrata, Arthropoda, &c.). (See Gener. Morphol., Bd. i. pp. 495-527.)

22. The Acentrica or Atypic Ground-Forms.--Among the acentrica or anaxonia are included all those ground-forms which are absolutely irregular, and in which neither a definite centre nor constant axes can be distinguished (e.g., most Sponges). These quite irregular ground-forms are very rare among the Radiolaria, but nevertheless there may be referred to them the amoeboid central capsule of some #Colloidea# (Collodastrum, p. 27, Pl. 3, figs. 4, 5) among the SPUMELLARIA, the irregular shells of many Collosphærida {xii}(Pl. 8, fig. 2), and the absolutely irregular shells of the Phorticida and Soreumida among the #Larcoidea#. (See Gener. Morphol., Bd. i. p. 400.)

23. The Subsidiary Groups of Geometrical Ground-Forms.--The four natural principal groups of ground-forms, which have just been defined according to the nature of the centre of their bodies, may be divided again into numerous subsidiary groups, defined by the relations of the constant axes and the two poles of each axis, as well as by the number of the axes and the differentiation of the secondary with respect to the principal axis. The most important of these subsidiary groups into which the principal ones are immediately divided are the following:--(1) The Centrostigma (or sphærotypic) are divided into spheres (Homaxonia) and endospherical polyhedra (Polyaxonia). (2) The Centraxonia (or grammotypic) into uniaxial (Monaxonia) and those with crossed axes (Stauraxonia); among the former of these may be distinguished the isopolar (phacotypic) and the allopolar (conotypic); among the latter the double and single pyramids. (3) The Centroplana (or bilaterals) are divided into amphipleura (or bilaterally radial) and zygopleura (or bilaterally symmetrical). (4) The Acentrica (or Anaxonia) or absolutely irregular ground-forms, present no special subdivisions.

For a complete system of the geometrical ground-forms and their relation to promorphological classification, see Gener. Morphol., Bd. i. pp. 555-558.

24. The Spherical or Homaxon Ground-Form.--The spherical is the only absolutely regular ground-form, since only in it are all axes which pass through the centre equal; it is very often realised among the Radiolaria, especially in the SPUMELLARIA and ACANTHARIA, where it furnishes the common original ground-form, but it is often to be seen in the shells of many PHÆODARIA (in most #Phæosphæria#); on the other hand, it is never found among the NASSELLARIA. Geometrical spheres, in the strict sense of the term, are only to be found among the SPUMELLARIA and ACANTHARIA, namely, in the central capsule of many #Collodaria# (Pls. 1, 2) and all #Sphæroidea# (Pls. 11-30) as well as many Acanthometra and Acanthophracta (Pls. 128-138). Nevertheless, speaking generally, one includes those central capsules and skeletons which have been distinguished here as endospherical polyhedra. (On these ground-forms see Gener. Morphol., Bd. i. pp. 404-406.)