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:--_
+-----------------------------------------------------------------+
| FIRST SUBCLASS. |
+-----------------------------------------------------------------+
| PORULOSA vel HOLOTRYPASTA. |
| |
| Central capsule originally spherical, without osculum or |
| principal opening, with innumerable fine pores. |
+-----------------------------------------------------------------+
| Legion I. | Legion II. |
| SPUMELLARIA. | ACANTHARIA. |
| (PERIPYLEA). | (ACTIPYLEA). |
+--------------------------------+--------------------------------+
| _Central capsule_ | _Central capsule_ |
| originally spherical, | originally spherical, |
| homaxon. | homaxon. |
| | |
| _Capsule-membrane_ | _Capsule-membrane_ |
| single, | single, |
| pores innumerable, | pores numerous, |
| distributed all over. | regularly distributed. |
| | |
| _Nucleus_ central, | _Nucleus_ excentric, |
| originally spherical | (usually dividing early). |
| (usually dividing late). | |
| | |
|_Skeleton_ absent or siliceous, | _Skeleton_ always of acanthin, |
| never centrogenous. | always centrogenous. |
| | |
| _Calymma_ always | _Calymma_ always |
| without phæodium. | without phæodium. |
+-----------------------------------------------------------------+
| SECOND SUBCLASS. |
+-----------------------------------------------------------------+
| OSCULOSA vel MEROTRYPASTA. |
| |
| Central capsule originally monaxon, with an osculum at |
| the basal pole of the vertical main axis. |
+-----------------------------------------------------------------+
| Legion III. | Legion IV. |
| NASSELLARIA. | PHÆODARIA. |
| (MONOPYLEA). | (CANNOPYLEA). |
+--------------------------------+--------------------------------+
| _Central capsule_ | _Central capsule_ |
| originally ovoid, | always spheroidal, |
| monaxon. | monaxon. |
| | |
| _Capsule-membrane_ | _Capsule-membrane_ |
| single, | always double, |
| a porous area | an astropyle |
| (porochora) at the oral | (with radiate operculum) |
| pole of the main axis. | at the oral pole |
| | of the main axis. |
| | |
| _Nucleus_ excentric, | _Nucleus_ always spheroidal, |
| near the aboral pole | in the main axis |
| (dividing late). | (dividing late). |
| | |
| _Skeleton_ siliceous, | _Skeleton_ of a silicate, |
| usually monaxon, | always extracapsular. |
| extracapsular. | |
| | |
| _Calymma_ always | _Calymma_ always |
| without phæodium. | with phæodium. |
+-----------------------------------------------------------------+
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.)
25. _The Endospherical Polyhedral Ground-Form._--The endospherical
polyhedron or polyaxon ground-form naturally follows the spherical or
homaxon. Under it are included all polyhedra whose angles fall in the
surface of a sphere; this ground-form is especially common among the
SPUMELLARIA, especially in the shells of #Sphæroidea#, but is also found
among the ACANTHARIA (especially in the Astrolophida and #Sphærophracta#),
as well as among the #Phæosphæria# (in most genera of the Orosphærida,
Sagosphærida, and Aulosphærida). Strictly speaking, all those
lattice-shells which have {xiii}been incorrectly called "spherical" belong
to this category, for they are none of them true spheres in the geometrical
sense (like the central capsules of the #Sphæroidea#), but rather
endospherical polyhedra, whose angles are indicated by the nodal points of
the lattice shell, or the radial spines which spring from them. These
endospherical polyhedra may be divided into three groups, the regular,
subregular, and irregular. Of _regular polyhedra_, properly so-called, it
may be shown geometrically that only five can exist, namely, the regular
tetrahedron, cube, octahedron, dodecahedron, and icosahedron. All these are
actually manifested among the Radiolaria, although but seldom. Much more
common are the _subregular endospherical polyhedra_, _e.g._, spherical
lattice-shells with regular hexagonal meshes of equal size; they are never
exactly equal nor perfectly regular, but the divergences are so
insignificant that they escape superficial observation (Pl. 20, figs. 3, 4;
Pl. 26, figs. 1-3). On the contrary in the _irregular endospherical
polyhedra_ the meshes of the lattice-sphere are more or less different in
size and often in form also (Pl. 28, figs. 4, 8; Pl. 30, figs. 4, 6). The
five truly regular polyhedra require separate notice on account of their
importance. (See Gener. Morphol., Bd. i. p. 406.)
26. _The Regular Icosahedral Ground-Form._--The ground-form whose
geometrical type is the regular icosahedron (bounded by twenty equilateral
triangles) is rarely exemplified, but it occurs among the PHÆODARIA in the
Circoporid genus _Circogonia_ (Pl. 117, fig. 1), and also in certain
Aulosphærida, but, apparently, only as an accidental variation (_e.g._,
_Aulosphæra icosahedra_). Furthermore, this ground-form may also be assumed
to occur in those #Sphæroidea# whose spherical lattice-shells bear twelve
equidistant radial spines (_e.g._, many species of _Acanthosphæra_,
_Heliosphæra_, and other Astrosphærida); the basal points of these spines
indicate the twelve angles of the regular icosahedron. (See on this head
Gener. Morphol., Bd. i. p. 411.)
27. _The Regular Dodecahedral Ground-Form._--The ground-form whose
geometrical type is the regular dodecahedron (or pentagonal dodecahedron),
bounded by twelve equilateral and equiangular pentagons, is very rarely
found perfectly developed, as in _Circorrhegma dodecahedra_ (Pl. 117, fig.
2). This form is by no means so common among the Radiolaria as in the
pollen grains of plants (_e.g._, _Buchholzia maritima_, _Fumaria spicata_,
_Polygonum amphibium_, &c.). It can, however, be regarded as present in all
those #Sphæroidea# whose spherical lattice-shells bear twenty equal and
equidistant radial spines (_e.g._, many species of _Acanthosphæra_,
_Heliosphæra_, and other Astrosphærida); the basal points of these spines
mark out the twenty angles of the regular pentagonal dodecahedron. (See
Gener. Morphol., Bd. i. p. 412.)
28. _The Regular Octahedral Ground-Form._--The ground-form whose
geometrical type is the regular octahedron (bounded by eight equilateral
triangles), commonly appears among the SPUMELLARIA in the family
Cubosphærida (p. 169, Pls. 21-25). In {xiv}these #Sphæroidea# the typical
ground-form is usually indicated by six equal radial spines, which are
opposed to each other in pairs, and lie in three similar axes perpendicular
to each other; these are the three axes of the tesseral crystallographic
system; one of them is vertical, whilst the other two cross each other at
right angles in its centre. Occasionally, too, the spherical form of the
lattice-shell passes over into that of the regular octahedron (Pl. 22,
figs. 8, 10). The same form recurs in _Circoporus_ (Pl. 117, fig. 6) among
the PHÆODARIA. In the vegetable kingdom it is exhibited by the antheridia
of _Chara_. It is not found in the NASSELLARIA and ACANTHARIA. (See Gener.
Morphol., Bd. i. p. 412.)
29. _The Regular Cubic Ground-Form._--The ground-form whose geometrical
type is that of a die or cube, is actually presented in a very striking
manner by various Radiolaria. Among the SPUMELLARIA it occurs in certain
#Sphæroidea#, _e.g._, in the Astrosphærid genera _Centrocubus_ and
_Octodendron_ (Pl. 18, figs. 1-3); in these the central medullary shell is
a complete cube, bounded by six equal squares, from the eight angles of
which eight equal radial spines project. This form can also be regarded as
present in those #Sphæroidea# whose spherical lattice-shell bears eight
equal and equidistant radial spines (many Astrosphærida). Besides these the
cubic ground-form is to be seen in certain NASSELLARIA of the family
Tympanida, especially in _Lithocubus_ (Pl. 82, fig. 12; Pl. 94, fig. 13),
in many species of _Acrocubus_, _Microcubus_, &c.; the twelve bars of its
lattice-skeleton correspond often exactly to the edges of the cube. (See
Gener. Morphol., Bd. i. p. 413.)
30. _The Regular Tetrahedral Ground-Form._--The ground-form whose
geometrical type is the regular tetrahedron, bounded by four equilateral
triangles, occurs less frequently in the Radiolaria than the other four
regular polyhedra. Among the SPUMELLARIA it is found in the #Beloidea#, and
especially in those members of the Thalassosphærida and Sphærozoida whose
spicules bear four equal branches, diverging at equal angles from a common
centre. Precisely the same structure is seen also among the NASSELLARIA in
some #Plectoidea#, as in _Tetraplagia_ among the Plagonida, and
_Tetraplecta_ among the Plectanida. The skeleton of both these genera
consists of four equal rods, which radiate at equal angles from a common
centre, just as do the axes of the regular tetrahedron. The tetrahedral
form of these #Plectoidea# is the more important and interesting since on
the one hand it is related to the similar spicular form of the #Beloidea#,
and on the other perhaps furnishes the starting point from which _Cortina_
among the NASSELLARIA may be derived (_Plagoniscus_, _Plectaniscus_). (See
Gener. Morphol., Bd. i. p. 415.)
31. _The Isopolar-Monaxon or Phacotypic Ground-Form._--The isopolar
uniaxial or phacotypic ground-form is characterised by the possession of a
vertical main axis with {xv}equal poles, whilst no transverse axes are
differentiated. All horizontal planes which cut the axis at right angles
are circles, and increase in size from the poles towards the equator. The
most important ground-forms of this group are the _phacoid_ (the lens or
oblate spheroid) and the _ellipsoid_ (or prolate spheroid). Phacoids (or
geometrical lenses with blunt margins) are very often presented by the
central capsules of the #Discoidea# and of many ACANTHARIA (Quadrilonchida
and Hexalaspida), but the lattice-shells of many SPUMELLARIA and ACANTHARIA
exhibit the same form, as also do a few PHÆODARIA (_e.g._, _Aulophacus_).
True geometrical ellipsoids are seen in the central capsules of many
#Prunoidea# among the SPUMELLARIA, and of many Amphilonchida and
Belonaspida among the ACANTHARIA. Furthermore, the lattice shells of many
species of these groups retain the same essential form, _e.g._, many
Ellipsida, Druppulida, and Spongurida (Pls. 13-17, and 39), as well as most
Belonaspida. (See Gener. Morphol., Bd. i. p. 422.)
32. _Allopolar-Monaxon or Conotypic Ground-Form._--The allopolar uniaxial
or conotypic ground-form is characterised by the possession of a vertical
main axis whose two poles are unlike, while no transverse axes are
differentiated. All horizontal planes cutting the main axis at right
angles are circles, and decrease more rapidly from the largest plane
towards the basal than towards the apical pole. The most important
ground-forms of this group are the ovoid, the cone, and the hemisphere.
They often occur (and in geometrical perfection) in the egg-shaped central
capsule and podoconus of the NASSELLARIA, as well as in the shells of
several groups of this legion, particularly in the Cyrtocalpida or
Monocyrtida eradiata (Pl. 51, figs. 10-13), and in many Stichocyrtida
eradiata; furthermore, they are also seen among the PHÆODARIA, _e.g._,
certain Challengerida (Pl. 99, figs. 19-22). (See Gener. Morphol., Bd. i.
p. 426.)
33. _The Regular Dipyramidal or Quadrilonchial Ground-Form._--The
ground-forms whose geometrical type is the regular double pyramid are
characterised by a vertical main axis which possesses equal poles, and
which is crossed at its centre by several equal transverse axes. The
horizontal equatorial plane is therefore a regular polygon, and divides the
body into two equal regular pyramids. The simplest and commonest form of
this group is the quadratic octahedron, the ground-form of the quadratic
crystallographic system; its equatorial plane is a square. This regular
dipyramidal ground-form occurs among the SPUMELLARIA in the shells of the
Staurosphærida as well as of many #Discoidea#, in which several equidistant
radial spines or arms lie in the quadratic equatorial plane of the body,
and project from the margin of the lenticular disc (_e.g._, _Sethostaurus_,
Pl. 31; _Histiastrum_, Pl. 46, &c.). It is, however, among the ACANTHARIA
that the most important part is played by this ground-form (and especially
by the quadratic octahedron); it forms the basis of all those
#Acanthometra# and #Acanthophracta# in which twenty radial spines are
disposed according to the Müllerian Law, and in which {xvi}the four
equatorial spines are of equal dimensions (Icosacantha). (See Gener.
Morphol., Bd. i. p. 436-446.)
34. _The Amphithect Dipyramidal or Lentelliptical Ground-Forms._--The
ground-forms whose geometrical type is the lenticular or "triaxial"
ellipsoid, may also be designated amphithect double pyramids; they are
characterised by the possession of a vertical main axis which has similar
poles, and is crossed at its middle by two transverse axes, unequal but
isopolar. The horizontal equatorial plane of the body is therefore an
amphithect or elongated polygon (a rhombus in the simplest case possible),
and divides the whole body into two equal amphithect pyramids. The simplest
and commonest form of this group is the rhombic octahedron, which is also
the ground-form of the rhombic crystallographic system. It plays an
important part in those ACANTHARIA in which twenty radial spines are
disposed according to the Müllerian Law, but in which the two pairs of
equatorial spines are unequal (different geotomical and hydrotomical axes,
see p. 719); to this category belong the Amphilonchida (Pl. 132),
Belonaspida (Pl. 136), Hexalaspida (Pl. 139), and Diploconida (Pl. 140). A
form essentially identical obtains also among the SPUMELLARIA in the
majority of the #Larcoidea#, both in their triaxial lattice-shells, and in
their lentelliptical central capsules, which present geometrically accurate
triaxial ellipsoids, with three unequal isopolar axes at right angles to
each other. (See Gener. Morphol., Bd. i. p. 446-452.)
35. _The Regular Pyramidal Ground-Forms._--The ground-forms whose
geometrical type is the regular pyramid, and which are the most conspicuous
in the Medusæ, Polyps, Corals, and regular Echinoderms (the Radiata of
earlier authors), are almost confined among the Radiolaria to the legion
NASSELLARIA; they occur, however, in the great majority of these, and
especially in those families which may be classed together as "#Cyrtoidea#
triradiata et multiradiata." Strictly speaking, however, almost all these
NASSELLARIA, at all events in their origin, are bilateral or dipleuric,
since the primary sagittal ring with its characteristic apophyses marks out
the sagittal median plane, and further, since the three feet of the basal
tripod are usually divided into an unpaired dorsal (pes caudalis) and two
paired ventral or lateral (pedes pectorales, dexter et sinister). On the
other hand, it is noteworthy, firstly, that among the primitive
#Plectoidea# there are perfectly regular radial forms, without any
indication of an original bilateral symmetry, and secondly, that similar
forms are also very common among the #Cyrtoidea#, probably as secondary
radial forms, developed from primitive bilateral ones. Similar cases also
occur in certain PHÆODARIA (_e.g._, the Medusettida and Tuscarorida, Pls.
100, 120), but they are entirely wanting among the ACANTHARIA and
SPUMELLARIA. The multiradial NASSELLARIA have arisen from the triradial by
the interpolation of three, six, nine, or more interradial and adradial
secondary apophyses between the three primary perradial ones. (See Gener.
Morphol., Bd. i. pp. 459-874.)
{xvii}36. _The Amphithect Pyramidal Ground-Forms._--The ground-forms whose
geometrical type is the amphithect pyramid, are distinguished from the
regular pyramidal forms, just discussed, chiefly by the form of the basal
plane, which is not a regular, but an amphithect or elongated polygon (in
the simplest case a rhombus). Hence in this case the allopolar main axis of
the body is crossed by two transverse axes which are isopolar and at right
angles, but are unequal; they cannot, however be distinguished as sagittal
and frontal axes as is the case in the zeugites. In the animal as well as
in the vegetable kingdom, an important part is played by this ground-form,
_e.g._, in the Ctenophora, where it is the rhombic pyramid. Among the
Radiolaria it is not common, though it is clearly expressed among the
NASSELLARIA in a number of #Stephoidea# (Stephanida and Tympanida), as well
as in many #Spyroidea# (_e.g._, the bipedal Zygospirida). It is very
accurately developed among the PHÆODARIA in the bivalved #Phæoconchia#
(Pls. 121-128), where the two valves of the shell (dorsal and ventral) are
generally exactly alike, their median keels corresponding to the poles of
the sagittal axis. In the slit between the two valves lie the two secondary
openings (right and left) of the tripylean central capsule, corresponding
to the two poles of the frontal axis, and the main axis stands
perpendicularly to both these, its oral pole being indicated by the
astropyle, or principal aperture. (See Gener. Morphol., Bd. i. pp.
479-494.)
37. _The Amphipleural Ground-Forms._--By the term amphipleural ground-forms
are to be understood those usually defined as "bilaterally radial"; their
geometrical type is a half amphithect pyramid. The best known examples of
this form in the animal kingdom are the bilateral five-rayed Echinoderms
(_Spatangus_, _Clypeaster_), in the vegetable kingdom the symmetrical
five-rayed flowers (_Viola_, _Trifolium_). The three dimensive axes have
the same relation as in the zygopleura, to be next discussed, and which
also resemble them in being divisible only by one plane (the sagittal
median plane) into two equal halves. They differ, however, the amphipleural
body not being made up of two antimeres, but of at least three pairs of
antimeres (or three parameres), being therefore primitively radial. Hence
each of the symmetrical halves of the body contains more than one antimere.
Among the Radiolaria this form does not occur in the SPUMELLARIA,
ACANTHARIA, or PHÆODARIA; it is very common, however, among the
NASSELLARIA; many #Cyrtoidea# multiradiata and #Spyroidea# multiradiata
show this bilaterally radial ground-form, inasmuch as the body consists of
two symmetrical halves, and is also composed of numerous (usually three,
six, nine, or more) radial parameres. In the multiradiate Dicyrtida and
Tricyrtida the cephalis (the first joint) is usually bilateral, whilst the
thorax (the second joint) is multiradial. (See Gener. Morphol., Bd. i. pp.
495-506.)
38. _The Zygopleural Ground-Forms._--As zygopleural or dipleural
ground-forms, as opposed to the amphipleural, are classed those zeugites or
centroplana which are known {xviii}as "bilaterally symmetrical" in the
strictest sense of the term. This is the most important ground-form in the
animal kingdom, inasmuch as it obtains almost exclusively among the higher
animals (Vertebrata, Articulata, Mollusca, Vermes). The body consists of
only two antimeres, which correspond to the two symmetrical halves of the
body. Of the three dimensive axes two are allopolar, one isopolar; the oral
pole of the longitudinal main axis is different from the aboral; the dorsal
pole of the sagittal axis is different from the ventral; but the right pole
of the frontal axis is equal to the left. The right antimere is usually
precisely similar to the left (Eudipleura), more rarely it is slightly
dissimilar or asymmetrical (Dysdipleura). Among the Radiolaria this
ground-form is entirely wanting in the Porulosa or Holotrypasta
(SPUMELLARIA and ACANTHARIA), but on the contrary it is very common in the
Osculosa or Merotrypasta (NASSELLARIA and PHÆODARIA). In the NASSELLARIA it
is of special importance, for the typical _Cortina_ (the combination of the
primary sagittal ring with the basal tripod) exhibits the zygopleural
ground-form clearly sketched out; indeed it is usually clearly seen even in
the sagittal ring itself, for its ventral segment is more strongly curved
than the dorsal; its basal (or oral) pole is always different from the
apical (or aboral). Of the three feet of the basal tripod the unpaired
(caudal) one is directed dorsally and backwards, the two paired (pectoral)
ones ventrally and forwards. The majority of the NASSELLARIA may be
regarded as modifications of this original ground-form. Its relation to the
primitively triradiate tripod presents a still unsolved problem, and the
numerous relations of the zygopleural to the multiradiate ground-forms in
the NASSELLARIA are exceedingly complicated. The zygopleural ground-form is
less widely distributed among the PHÆODARIA, though it is very
characteristically developed in the rich and varied group of Challengerida
(Pl. 99). (See Gener. Morphol., Bd. i. pp. 507-527.)
39. _Synopsis of the Geometrical Ground-Forms:--_
Principal Groups of Ground-Forms.
Subsidiary Groups of Ground-Forms.
Geometrical Type.
Examples.
I. CENTROSTIGMA.
The geometrical centre of the body is a point. Main axis wanting.
|
+-I. HOMAXONIA.
| All axes equal.
| |
| +-1. _Sphere_,
|
| Central capsule of the #Sphæroidea# and of many ACANTHARIA.
|
+-II. POLYAXONIA.
Endospherical polyhedra. All the angles of the body lie on the surface
of a sphere. Numerous isopolar axes.
|
+-2. _Endospherical polyhedron_,
|
| Lattice-spheres of the #Sphæroidea#, #Sphærophracta#, and
| #Phæosphæria#.
|
+-3. _Icosahedron_,
|
| _Circogonia_.
|
+-4. _Dodecahedron_,
|
| _Circorrhegma_.
|
+-5. _Octahedron_,
|
| Cubosphærida, _Circoporus_.
|
+-6. _Cube_,
|
| _Centrocubus_, _Lithocubus_, &c.
|
+-7. _Tetrahedron_,
_Tetraplagia_, _Tetraplecta_, &c.
II. CENTRAXONIA. {xix}
The geometrical centre of the body is a straight line (the vertical main
axis).
Constant transverse axes (perpendicular to the main axis) are wanting in
the Monaxonia (which have circular transverse sections); on the contrary
they are differentiated in the Stauraxonia (which have polygonal
transverse sections).
|
+-III. MONAXONIA.
| Uniaxial ground-forms or centraxonia without transverse axes. The
| transverse planes (perpendicular to the main axis) are circles.
| |
| +-8. _Monaxonia isopola._
| | (Spheroids and ellipsoids; both poles of the main axis similar.)
| |
| | Central capsule and lattice-shell of of many #Discoidea# (lenses) and
| | #Prunoidea# (ellipsoids), Belonaspida, &c.
| |
| +-9. _Monaxonia allopola._
| (Cone, ovoid and hemisphere; the two poles of the axis dissimilar.)
|
| Central capsule and lattice-shell of many NASSELLARIA, especially
| the #Cyrtoidea# eradiata (Cyrtocalpida, &c.).
|
+-IV. STAURAXONIA.
Pyramidal ground-forms or centraxonia with transverse axes. The
transverse planes (perpendicular to the main axis) are either regular
or amphithect polygons.
|
+-10. _Dipyramides regulares._
| (Quadratic octahedron, or quadrilonchial forms and regular double
| pyramids.)
|
| ACANTHARIA with twenty radial spines, the four equatorial being
| equal. Multiradial #Discoidea# and Staurosphærida.
|
+-11. _Dipyramides amphithectæ._
| (Rhombic octahedron, lentellipsoid, and amphithect double pyramids.)
|
| ACANTHARIA with twenty radial spines, whose four equatorial spines
| are unequal but paired. Many #Larcoidea#.
|
+-12. _Pyramides regulares._
| (Regular pyramids.)
|
| Many NASSELLARIA (triradial and multiradial). Medusettida and
| Tuscarorida.
|
+-13. _Pyramides amphithectæ._
(Rhombic pyramids.)
#Phæoconchia#. Bipedal #Spyroidea# and #Stephoidea#.
III. CENTROPLANA.
The geometrical centre of the body is a plane (the sagittal plane).
Constant transverse axes (perpendicular to the main axis) are wanting in
the Monaxonia (which have circular transverse sections); on the contrary
they are differentiated in the Stauraxonia (which have polygonal
transverse sections).
|
+-V. BILATERALIA (or ZEUGITA).
Bilateral forms in the general sense, with right and left halves.
|
+-14. _Amphipleura_
| (Bilaterally radial ground-form.)
|
| Many #Cyrtoidea# and #Spyroidea# multiradiata.
|
+-15. _Zygopleura._
(Bilaterally symmetrical ground-form.)
Most NASSELLARIA (primitively at least), many Challengerida.
IV. ACENTRA.
There is no geometrical centre.
|
+-VI. ANAXONIA.
No definite axes can be determined.
|
+-16. _Irregularia._
(Absolutely irregular ground-forms.)
_Collodastrum_, _Collosphæra_, Phorticida, Soreumida.
40. _Mechanical Causes of the Geometrical Ground-Forms._--The great variety
of ground-forms exhibited by the Radiolaria is of special interest, since
in most instances their causes admit of recognition, and since they are so
intimately related to each other that even in the remaining cases the
assumption that they have arisen by purely mechanical _causæ efficientes_
seems justified. In this respect the first rank is taken by statical
conditions, especially the indifferent or stable equilibrium of the whole
organism, which floats freely in the water. With regard to these
fundamental statical relations, three principal groups of ground-forms may
be distinguished, pantostatic, polystatic, and monostatic.
41. _Pantostatic Ground-Forms._--By pantostatic or indifferently stable
ground-forms are meant those in which the centre of gravity coincides with
the centre of the body, so that they are in equilibrium in any given
position. Strictly speaking, the only form which possesses perfectly
indifferent equilibrium is the sphere, that being the only truly homaxon
and perfectly regular form. Nevertheless, in a somewhat wider sense many
Polyaxonia, especially the endospherical polyhedra with very numerous
sides, may be {xx}included in this category. Such indifferently stable
bodies are found among the SPUMELLARIA in many #Collodaria# and
#Sphæroidea#, as well as in the Astrolophida among the ACANTHARIA. On the
contrary they are entirely wanting among the NASSELLARIA and PHÆODARIA,
since their central capsule constantly presents a main axis with a
differentiated basal pole, and determines the position of stable
equilibrium.
42. _Polystatic Ground-Forms._--Those ground forms are defined as
polystatic or multistable in which the body is in equilibrium in several
different positions (though not in an infinite number). The number of these
positions is usually twice as many as that of the constant equal isopolar
axes exhibited by the form. Hence the regular polyhedra have as many
positions of equilibrium as they have angles or sides, the icosahedron
twenty, dodecahedron twelve, octahedron eight, cube six, tetrahedron four.
The isopolar monaxon ground-forms (lens, ellipsoid, cylinder) and the
diplopyramidal ground forms (quadrilonchial and lentelliptical) have two
positions of stable equilibrium, since the two poles of the vertical axis
are equal and similar and the body is divided into equal halves by the
equatorial plane. This is the case in many SPUMELLARIA (especially
#Discoidea#, #Prunoidea#, and #Larcoidea#), as well as in the great
majority of ACANTHARIA. Perhaps the same holds good also in certain
NASSELLARIA (_e.g._, isopolar Tympanida) and PHÆODARIA (_e.g._, isopolar
#Phæosphæria#), though here unistable equilibrium appears to be
necessitated by the constant main axis of the central capsule and the
differentiated basal pole of the main axis.
43. _Monostatic Ground-Forms._--Those ground-forms are classed as
monostatic or unistable in which the body is in equilibrium only in one
position, since the centre of gravity of the body lies in a constant
vertical axis below its centre. This fixed position is only rarely and
exceptionally found among the SPUMELLARIA (_e.g._, in _Xiphostylus_,
_Sphærostylus_, _Lithomespilus_, _Lithapium_) and among the ACANTHARIA
(_e.g._, in _Zygostaurus_ and _Amphibelone_). On the contrary it is quite
usual among the NASSELLARIA and PHÆODARIA (with but few exceptions); for
here a vertical main axis, with a differentiated basal pole, is determined
even by the formation of the central capsule, and usually also by the
corresponding structure of the skeleton. Among the NASSELLARIA this basal
pole, with the porochora of the central capsule, appears always to be the
lower; as also in most #Phæogromia# among the PHÆODARIA. In the peculiar
bivalved #Phæoconchia#, on the other hand, the basal pole with the
cannopyle is directed upwards; as also in the Challengerida and
Tuscarorida. The #Phæosphæria# and #Phæocystina# are probably to a large
extent polystatic. In general unistable equilibrium may be assumed in the
following categories of ground-forms:--(1) Allopolar monaxon (conical and
ovoid); (2) pyramidal (regular and amphithect); (3) Centroplana
(amphipleura and zygopleura); (4) Anaxonia.
{xxi}44. _Principal Axes._--From the foregoing consideration of the
statical conditions and their direct causal connection with the geometrical
ground-forms of the Radiolaria, the great mechanical significance of the
differentiation of definite axes in these unicellular free-swimming
organisms will be manifest. The most important of these is the primary main
axis (axis principalis, or protaxon), which in all cases has a vertical
direction. It is wanting in the Centrostigma (spheres and endospherical
polyhedra), and in the Anaxonia (acentra). It is isopolar in the phacotypic
forms (Monaxonia isopola), and in the double pyramids (Stauraxonia
isopola). It is allopolar in all monastatic ground-forms, in the conotypic
forms (Monaxonia allopola), pyramids (Stauraxonia allopola), and the
Centroplana (or bilateral forms).
45. _Secondary or Transverse Axes._--In contrast to the vertical main axis
all the other constant axes differentiated in the body may be called
"secondary axes," or "transverse axes," since they cross the former at
definite points. All ground-forms whose vertical axis is crossed by a fixed
number of such axes at definite angles may be called "Stauraxonia." They
are divided into two groups, double pyramids and single pyramids; in the
former the two poles of the main axis (or the two halves of the body
separated by the equatorial plane) are similar (Stauraxonia homopola), in
the latter dissimilar (Stauraxonia heteropola). If all the secondary axes
be equal, the stauraxon ground-form is regularly radial. If some of them be
unequal they are arranged in certain relations towards two primary
transverse axes, perpendicular to each other, to which all the other
secondary axes are subsidiary; the ground-forms are then either amphithect
or bilateral. The two primary transverse axes, which may also be designated
"ideal transverse axes" (euthyni), divide the vertical main axis in its
centre; one of them is the sagittal, the other the frontal. These three
dimensive axes give the factors which accurately determine the ground-form
and the dimensions in most Radiolaria; the vertical main axis determines
the length (principal axis); one horizontal transverse axis determines the
thickness (sagittal axis), and the other the breadth (frontal axis). Those
ground-forms in which the transverse axes are isopolar are termed
"amphithect," and those in which the one (frontal or lateral) is isopolar
and the other (sagittal or dorso-ventral) is allopolar, are termed
"bilateral," or better "zeugitic."
46. _Primary and Secondary Ground-Forms._--The geometrical sphere must be
regarded as the original ground-form of the Radiolaria; it being understood
that its monophyletic derivation from a single stem-form, _Actissa_, is
correct. The simplest forms of _Actissa_ (_Procyttarium_, Pl. 1, fig. 1)
are in fact geometrically _perfect spheres_; indeed even the individual
parts which compose their unicellular bodies (nucleolus, nucleus, central
capsule and calymma) are concentric spheres. But in addition the central
capsules of most other SPUMELLARIA, especially the #Sphæroidea#, as well as
of many ACANTHARIA {xxii}are true spheres. Furthermore the simple or
concentrically composed lattice-spheres of #Sphæroidea#, #Sphærophracta#,
and #Phæosphæria# may be regarded as spheres, although strictly speaking
they are endospherical polyhedra. From the primary spherical form of the
Radiolaria all other secondary forms may be derived in the following
order:--1. By the development of a main axis the Monaxonia arise. 2. By the
development of transverse axes the Stauraxonia arise. 3. In both groups
(Monaxonia and Stauraxonia) the two poles (or upper and lower halves of the
body) are at first similar (Isopola). 4. By differentiation in the two
poles or halves of the body (distinction between the basal pole and the
apical) the forms with different poles (Allopola) arise. 5. The transverse
axes of the Stauraxonia are at first equal (regular pyramids and double
pyramids). 6. By differentiation in the transverse axes (distinction
between the sagittal and the frontal axis) the amphithect pyramids and
double pyramids arise. 7. From the amphithect pyramids the Amphipleura
arise by differentiation of both poles of the sagittal axis. 8. The
zygopleural ground-form appears last, as the simplest form of the
Amphipleura.
47. _The Ground-Forms of the Spumellaria._--The SPUMELLARIA, being the
oldest and most primitive Radiolaria, have for the most part either
indifferent or multistable equilibrium; _e.g._, all #Colloidea# and
#Beloidea# which have a spherical central capsule, and also most
#Sphæroidea#. Among these primitive Centrostigma true spheres and
endospherical polyhedra are represented in the utmost variety, and the
regular polyhedra in particular. By the development of a vertical main axis
these Centrostigma have also given rise to very numerous Centraxonia, which
are usually isopolar, very rarely allopolar. Sometimes they are Monaxonia
(circular in transverse section), sometimes Stauraxonia (polygonal in
transverse section). The vertical main axis is longer in the #Prunoidea#,
shorter in the #Discoidea# than any of the other axes. The #Larcoidea# are
distinguished by their lentelliptical or triaxial ellipsoid form; the three
different but isopolar axes corresponding with those of the rhombic
octahedron; but even among the #Sphæroidea#, #Prunoidea#, and #Discoidea#,
this form is sometimes produced by the differentiation of two different
transverse axes at right angles to each other. Whilst these ground-forms
(Centraxonia and Centrostigma) occur in the utmost variety among the
SPUMELLARIA, the centroplanar (or true bilateral) ground-form is entirely
wanting.
48. _The Ground-Forms of Acantharia._--In the small family Astrolophida,
which contains the most archaic forms of the legion (_Actinelius_,
_Astrolophus_), the ACANTHARIA show a direct relation to the most primitive
SPUMELLARIA (_Actissa_), and like these have indifferent equilibrium; their
central capsule is a sphere, their calymma an endospherical polyhedron,
whose angles are indicated by the distal ends of the numerous {xxiii}equal
radial spines. In the great majority of ACANTHARIA, however (all
#Acanthonida# and #Acanthophracta#), twenty radial spines are present,
regularly distributed, according to Müller's icosacanthan law, in five
parallel circles, each containing four crossed spines (p. 717). Usually the
twenty spines are equal, and the ground-form is the quadratic octahedron,
or a regular double pyramid with sixteen sides. But in some groups (the
Amphilonchida and Prunophracta) two opposite equatorial spines are much
more strongly developed than the other eighteen, and therefore the
hydrotomical axis in the equatorial plane is larger than the geotomical
axis (p. 719); the isopolar stauraxonian form passes over into the
allopolar, and the ground-form becomes the rhombic octahedron or the
amphithect double pyramid (compare §§ 33 and 34, and p. 720). The
centroplanar ground-form is entirely wanting in the ACANTHARIA.
49. _The Ground-Forms of the Nassellaria._--The NASSELLARIA all possess
monostatic ground-forms, inasmuch as by the very structure of their
monopylean central capsule a vertical main axis is necessitated, whose
basal pole occupies the porochora. The same arrangement is also for the
most part clearly recognisable in the corresponding structure of the
skeleton, which is generally either centraxon or centroplanar. Among their
manifold skeletal forms different larger groups of ground-forms may be
recognised according as the vertical allopolar main axis is crossed by
differentiated transverse axes or not (Stauraxonia or Monaxonia); the
former are either triradial or multiradial. The triradial, with three
lateral or terminal radial apophyses, constitute the greater part of the
NASSELLARIA, and have probably been derived originally from the triradial
#Plectoidea# (_Triplagia_, _Triplecta_); a more careful examination,
however (especially with reference to the structure of the cortinar
septum), reveals the fact that the ground-form is not strictly regularly
pyramidal (with three equal radii), but amphipleural (with two paired
ventral and one unpaired dorsal radius), and that it usually passes over
into a distinctly zygopleural form. The same holds true of the multiradial
NASSELLARIA, where for the most part three interradial or six adradial
(sometimes more) apophyses are intercalated between the three primary
perradial ones; sometimes here also the ground-form is a quite regular
hexagonal or nonagonal pyramid, but usually it is more or less amphithect
or amphipleural. Among the eradial NASSELLARIA, which have no radial
apophyses, the ground-form is sometimes allopolar monaxon (conical, ovoid,
hemispherical, &c.), sometimes amphithect pyramidal (even in the simplest
Stephanida, _Archicircus_, &c.), or sometimes distinctly zygopleural or
bilateral (many #Plectellaria#).
50. _The Ground-Forms of the Phæodaria._--The PHÆODARIA agree with the
NASSELLARIA in the possession of a primitively centraxon ground-form, and
like them are monostatic, since a vertical main axis whose basal pole
passes through the astropyle is present, owing to the characteristic
structure of their cannopylean central capsule. In {xxiv}the great majority
of PHÆODARIA the spheroidal central capsule also possesses a pair of
parapylæ near the opposite apical pole of the main axis (Tripylea), and
these determine (as the right and left secondary openings) an isopolar
frontal axis. Hence, strictly speaking, in most PHÆODARIA the central
capsule has the geometrical ground-form of the amphithect pyramid (as in
the Ctenophora), with an allopolar vertical main axis, and two unequal, but
isopolar, horizontal transverse axes. In many PHÆODARIA the skeleton also
has this amphithect pyramidal ground-form, _e.g._, the bivalved
#Phæoconchia# and part of the #Phæogromia#. On the contrary, in the rest of
the PHÆODARIA the skeleton exhibits very various geometrical ground-forms,
independent of that of the central capsule. In the #Phæosphæria# it forms
preferably spheres or endospherical polyhedra, as also in the Castanellida
and Circoporida among the #Phæogromia#; among the Circoporida there are
also seen with remarkable distinctness the regular polyhedra (especially
the dodecahedron and icosahedron). Isopolar monaxonia are found among the
Aulosphærida (_Aulatractus_) and Orosphærida; allopolar monaxonia among the
Challengerida (_Lithogromia_). The Medusettida and Tuscarorida show various
forms of regular pyramids (allopolar Stauraxonia); and finally, the
Challengerida are for the most part centroplanar or bilateral. Thus the
PHÆODARIA present a great wealth of different geometrical ground-forms in
the development of their skeleton, not in that of their central capsule.