192. Phylogeny of the Phæodaria.—The legion Phæodaria or Cannopylea is so clearly marked off from other Radiolaria by the double membrane of the central capsule and the astropyle at its oral pole, as well as by the extracapsular phæodium, that it must be regarded phylogenetically as an independent stem (§ 9). This stem is only connected at its root by Phæodina with the stem-form of the Spumellaria, Actissa. The stem itself is monophyletic, inasmuch it its members may be derived without violence from the skeletonless Phæodinida (Phæodina, Phæocolla). On the other hand, the formation of the skeleton of the Phæodaria is undoubtedly polyphyletic, different Phæodinida having independently commenced the formation of a skeleton and having carried it out in very different ways.
193. Origin of the Phæodaria.—The Phæodinida (p. 1544, Pl. 101), which may naturally be regarded as the common stem-group of the Phæodaria, have their nearest relations among other Radiolaria in the Thalassicollida (p. 10); and since this family is to be regarded as the primitive group of all Radiolaria, they may be directly derived from them phylogenetically. The essential modifications by which the primitive Phæodinida have arisen from the more archaic Thalassicollida are of three kinds; (1) the doubling of the membrane of the central capsule; (2) the reduction of the numerous fine pores in the membrane and the formation of an osculum, and of an astropyle closing it, at the oral pole of the main axis; (3) the production of an extracapsular phæodium. This last may, perhaps, be regarded as a unilateral hypertrophy of the voluminous pigment masses which are deposited in the sarcomatrix of certain Thalassicollida. Of the two genera of Phæodinida hitherto known, probably Phæodina (Pl. 101, fig. 2) approaches the original stem of the Phæodaria more nearly than Phæocolla (Pl. 101, fig. 1), for the latter exhibits only the large main opening of the central capsule (astropyle), whilst the former possesses also a pair of accessory openings (parapylæ). The hypothetical stem-form (Phæometra) presumably had a larger number of small parapylæ (like many Circoporida and Tuscarorida), and the astropyle was probably but little differentiated from them.
194. Hypothetical Genealogical tree of the Phæodaria:—
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| Phæosphæria | Cœloplegmida | Phæogromia | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Aularida | Tuscarorida | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Cœlodrymida | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Aulonida | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Cœlotholida Cœlographida |
Haeckelinida | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Conchopsida | Cœlodorida | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Aulosphærida | Cœlodendrida | Circogonida | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Conchasmida Concharida |
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| Sagmarida | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Castanellida | Circoporida | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Cannosphærida | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Oroscenida | Concharida | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Sagenida Sagophærida |
Gazellettida | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Oronida Orosphærida |
Pharyngellida | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Euphysettida Medusettida |
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| Lithogromida | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Challengerida | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Phæodinida | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Aulacanthida | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Cannobelida | Catinulida | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Dictyochida | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Phæodinida | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Cannorrhaphida | Phæodinida | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Phæodina | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Actissa | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Phæosphæria | Cœloplegmida | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Aularida | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Cœlodrymida | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Aulonida | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Cœlotholida Cœlographida |
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| Conchopsida | Cœlodorida | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Aulosphærida | Cœlodendrida | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Conchasmida Concharida |
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| Sagmarida | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Cannosphærida | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Oroscenida | Concharida | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Sagenida Sagophærida |
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| Oronida Orosphærida |
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| Phæodinida | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Phæogromia | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Tuscarorida | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Haeckelinida | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Circogonida | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Castanellida | Circoporida | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Gazellettida | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Pharyngellida | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Euphysettida Medusettida |
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| Lithogromida | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Challengerida | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Aulacanthida | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Cannobelida | Catinulida | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Dictyochida | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Phæodinida | ≈ | Phæodinida | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Cannorrhaphida | Phæodinida | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Phæodina | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Actissa | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
195. Phæocystina and Phæocoscina.—Whilst the malacoma of all Phæodaria possesses the characteristics of the legion, and hence justifies the assumption of a monophyletic origin, the skeleton, on the other hand, shows in the different groups such manifold and fundamental variations that a polyphyletic origin of the latter is indubitable. Different Phæodinida have commenced the formation of the skeleton independently, and it has progressed in different directions. In the Phæocystina it remained incomplete and led to the formation of various Beloid skeletons, whilst the Phæocoscina developed complete lattice-shells. Both of these divisions too are to be regarded as polyphyletic, since the skeletal forms of the different groups cannot be derived without violence from a common primitive form.
196. Phæocystina with a Beloid Skeleton.—The order Phæocystina includes all Phæodaria which have no complete lattice-shell; it contains, firstly, the skeletonless Phæodinida (the common stem-group of the legion), and secondly, the Phæacanthida, or Phæodaria with a Beloid skeleton (§ 115). The latter are divisible into several very different groups (at least two or three) which are probably different in origin. The Aulacanthida (Pls. 102-105) form radial tubes which perforate the calymma, their proximal end resting upon the surface of the central capsule, whilst the distal extremity projects freely outwards. The skeleton of the Cannorrhaphida, on the other hand, is composed of many separate portions which are never radially arranged but are either placed tangentially to the surface of the calymma or scattered irregularly in its gelatinous mass. Furthermore, in the three subfamilies of which this family is composed, the individual skeletal portions are so different that they have probably arisen independently of each other; in the Cannobelida they form cylindrical tangential tubes (Pl. 101, figs. 3-5), in the Catinulida flat basin or cap-like structures (Pl. 117, fig. 8), in the Dictyochida hollow rings, from which small pyramids are developed by unilateral formation of lattice-work (Pl. 101, figs. 9-14; Pl. 114, figs. 7-12).
197. Phæosphæria with a Sphæroid Skeleton.—The order Phæosphæria includes those Phæodaria which possess a spherical (sometimes slightly modified) lattice-shell without the characteristic aperture of the Phæogromia. They have probably arisen independently of these, though they may have been derived from the Castanellida by loss of the shell-aperture, which was present originally. The four families which we have distinguished among the Phæosphæria, are so different in the structure of their lattice-shell that their phylogenetic connection is doubtful. In the Orosphærida (Pls. 106, 107) and the Sagosphærida (Pl. 108) the whole lattice-shell consists of a single piece and is unjointed (without astral septa); in the former it is very firm and massive, with thick laminated trabeculæ and polygonal meshes; in the latter it is very delicate and brittle, with filiform trabeculæ and large triangular meshes. On the other hand, the voluminous shell of the Aulosphærida (Pls. 109-111), and of the Cannosphærida (Pl. 112), is characterised by a very peculiar system of joints; it is composed of numerous separate cylindrical tubes, which are placed tangentially and united at the nodes by stellate partitions or astral septa. The Cannosphærida possess further a simple central Cyrtoid shell, connected with the outer jointed shell by hollow radial trabeculæ. Since many Aulosphærida possess rudiments of such centripetal trabeculæ it is possible that these latter have been derived from the former by the loss of the central Cyrtoid shell; the formation of this monaxon shell perhaps indicates descent from the Phæogromia (Castanellida).
198. Phæogromia with a Cyrtoid Skeleton.—That order of the Phæodaria which we designate Phæogromia, contains many very different forms, all agreeing in the possession of a Cyrtoid skeleton, or a monaxon lattice-shell, which has a large aperture at one pole of its vertical main axis (§ 123). This Cyrtoid skeleton is sometimes ovoid or conical, sometimes lentiform or helmet-shaped, sometimes polyhedral or almost spherical. Although the principle of its structure is simple and often like that of the Monocyrtida among the Nassellaria, yet the structure of the wall and of the apophyses is so different in the various groups of the Phæogromia, that the order is probably polyphyletic, and its Cyrtoid shells have arisen independently of each other. Only in the Castanellida (Pl. 113) does the shell-wall usually consist of simple lattice-work; in the Challengerida, on the other hand (Pl. 99), it has an extremely fine Diatom-like structure; in the Medusettida (Pls. 118-128) a peculiar alveolar structure, and in the Circoporida (Pls. 114-117) and Tuscarorida (Pl. 100) it possesses a characteristic porcellanous constitution (with tangential spicules in a porous cement-mass); in the latter of these groups the surface is smooth, in the former peculiarly tabulate; the two families have also different stem-forms.
199. Phæoconchia with a Conchoid Shell.—The order Phæoconchia (Pls. 121-128) is separated not only from all other Phæodaria, but also from all other Radiolaria, by the possession of a bivalved shell resembling that of a Lamellibranch; the two valves of this Conchoid skeleton are to be interpreted as dorsal and ventral (§ 128). Probably these bivalved shells are independent products, but possibly they may have been formed by the bisection of a simple spherical lattice-shell; in the former case the Phæoconchia would be directly descended from the Phæodinida, in the latter from the Castanellida. The three families which we have distinguished among the Phæoconchia, probably constitute a connected stem, the most primitive group of which are the Concharida (Pls. 123-125). From these the Cœlodendrida (Pls. 121, 122) have next arisen by the formation of a "galea" upon the apex of each valve, and the growth of hollow tubes from this helmet-like structure. Finally, the Cœlographida (Pls. 120-128) have been developed from the Cœlodendrida by the formation of a basal nasal tube (rhinocanna) from each galea, and the formation of a median or paired frenulum, which connects the opening of the nasal tube with the apex of the galea. In the Cœlodendrida, as well as in the Cœlographida, there are two different subfamilies, of which the more primitive (Cœlodorida, Cœlotholida) have free branches from the hollow radial tubes, whilst the more recent (Cœlodrymida, Cœloplegmida) form an outer bivalved shell by anastomosis of the branches of the tubes.
200. The Fundamental Biogenetic Law.—The causal connection between ontogeny and phylogeny, which finds its most precise statement in the fundamental biogenetic law, holds in general for the Radiolaria as for all other organisms. In order to furnish direct proof of this, however, a complete empirical knowledge both of individual and of palæontological development would be necessary. In both these directions, as has been shown in the foregoing chapters, our knowledge of the Radiolaria is very incomplete and fragmentary, but still we are able to convince ourselves indirectly of the validity of the law as applied to Radiolaria by the aid of comparative anatomy. This is now so fully known to us (§§ 1-140) that we are able not only to draw a complete and satisfactory picture of their morphology, but also to arrive at most important conclusions regarding the ontogeny and phylogeny of the individual groups. As regards the formation of the multiform skeleton of the Radiolaria, most of the ontogenetic series of forms, with which we have become acquainted by comparative anatomy, are of palingenetic nature; that is, they are primarily due to inheritance and thus of direct phylogenetic significance. On the other hand, among the ontogenetic phenomena of the Radiolaria, as far as they have yet been investigated, only very few are cenogenetic, that is, brought about by adaptive modification and without direct significance as regards phylogeny.
201. Mechanism of the Functions.—The vital phenomena of the Radiolaria are dependent upon the mechanical functions of their unicellular body, and like those of all other organisms, are to be referred to physical and chemical natural laws. All processes which appear in the life of the Radiolaria are, therefore, ultimately to be explained by the attraction and repulsion of the smallest particles, which compose the different portions of their unicellular body; and the sensation of pleasure or the opposite is in its turn the exciting cause of these elementary movements. Many adaptive arrangements in the Radiolarian organism may produce the appearance of being the premeditated result of causes working towards an end ("zweckthätig," causæ finales), but as opposed to this deceptive appearance it must here be expressly stated that these may be recognised in accordance with the developmental theory as the necessary consequence of mechanical causes (causæ efficientes).
Our physiological acquaintance with the Radiolaria has by no means progressed so far as our morphological, so that the incomplete communications which are placed here for the sake of completeness must be regarded merely as preliminary fragments, not as fully elaborated results. Since my recent investigations have been mainly in the direction of morphology, I can add but little to the physiological conclusions, which I stated at length in my monograph twenty-four years ago (L. N. 16, pp. 127-165). Recently the vegetative physiology of the Radiolaria has been much advanced by the recognition of the symbiosis with the Xanthellæ (§ 205, L. N. 22, 39, 42). In addition Karl Brandt has recently (1885) published several important contributions to the physiology of the Polycyttaria or Sphaerozoea (L. N. 52).
202. Distribution of Functions.—The distribution of the functions among the various parts of the unicellular organism of the Radiolaria corresponds directly to their anatomical composition, so that physiologically as well as morphologically the central capsule and the extracapsulum appear as the two coordinated main components. On the one hand the central capsule with its endoplasm and enclosed nucleus is the central organ of the "cell-soul" (Zellseele), the unit regulating its animal and vegetative functions, and the special organ of reproduction and inheritance. The extracapsulum forms, on the other hand, by its calymma the protective envelope of the central capsule, the support of the soft pseudopodia and the substratum of the skeleton; the calymma acts also as a hydrostatic apparatus, whilst the radiating pseudopodia are of the greatest importance both as organs of nutrition and adaptation, as well as of motion and sensation (§ 15). If, however, the vital functions as a whole be divided in accordance with the usual convention into the two great groups of vegetative (nutrition and reproduction) and animal (motion and sensation), then the central capsule would be mainly the organ of reproduction and sensation, and the extracapsulum the organ of nutrition and motion.
The numerous separate vital phenomena, which by accurate physiological investigation may be distinguished in the unicellular Radiolarian organism, may be distributed in the above indicated conventional fashion into a few larger and several smaller groups; it must always be borne in mind, however, that these overlap in many respects, and that the division of labour among the different organs in these Protista is somewhat complicated, notwithstanding the apparent simplicity of their unicellular organization. A general classification of the groups of functions is difficult, because each individual organ discharges several different functions. Thus the central capsule is pre-eminently the organ of reproduction and inheritance, but not less (though less conspicuous) is its importance as the psychical central organ, the unit regulating the processes of sensation, motion, and also nutrition. In this last respect it is comparable to the nerve-centres of the Metazoa, whilst the peripheral nervous system of the latter (including the organs of sense and the muscles) are in the present instance represented by the pseudopodia, which are at the same time the most important organs of nutrition and adaptation. In the calymma also in similar fashion several different physiological functions are united.
203. Metastasis.—The functions of metastasis and nutrition have in all Radiolaria a purely animal character, so that these Rhizopoda from the physiological standpoint are to be regarded as truly unicellular animals, or Protozoa ("Urthiere"). Since they do not possess, like plants, the power of forming synthetically the compounds (protoplasm, carbohydrates, &c.) necessary for their sustenance, they are compelled to obtain them ready-formed from other organisms. Like other true animals they evolve carbon dioxide by the partial oxidation of those products, and hence they successively take up the oxygen necessary to their existence from their environment.
The question whether the Radiolaria are to be regarded as true animals I discussed fully from various points of view in 1862, and finally answered in the affirmative (L. N. 16, pp. 159-165). Afterwards, when in my Generelle Morphologie (1866) I sought to establish the kingdom Protista, I removed the Radiolaria along with the other Rhizopoda from the animal kingdom proper and placed them in the kingdom Protista (Bd. i. pp. 215-220; Bd. ii. p. xxix). Compare also my Protistenreich (L. N. 32) and my Natürliche Schöpfungsgeschichte (vii. Aufl., 1879, p. 364). Both these steps appear fully justified when considered in the light of our present increased knowledge. From the physiological standpoint the Radiolaria appear as unicellular animals, for in this respect the animal character of their metastasis (that proper to an oxidising organism) furnishes the sole criterion. On the other hand, from the morphological standpoint, they are to be classed as neutral Protista, for in this respect their unicellular character is the prominent feature, and distinguishes them from all true multicellular animals (Metazoa). Compare my Gastræa Theorie (1873, Jena. Zeitschr. für Naturwiss., Bd. viii. pp. 29, 53).
204. Nutrition.—The nutritive materials which the Radiolaria require for their sustenance, especially albuminates (plasma) and carbohydrates (starch, &c.), they obtain partly from foreign organisms which they capture and digest, and partly directly from the Xanthellæ or Philozoa, the unicellular Algæ, with which they live in symbiosis (§ 205). Zooxanthella intracapsularis, found in the Acantharia (§ 76), is probably of the same significance in this respect as Zooxanthella extracapsularis of the Spumellaria and Nassellaria (§ 90); and perhaps the same is true also of Phæodella extracapsularis (or Zoochlorella phæodaris?) of the Phæodaria (§ 89). The considerable quantity of starch or amyloid bodies, elaborated by these inquiline symbiontes, as well as their protoplasm and nucleus, are available, on their death, for the nutrition of the Radiolaria which harbour them. Nutrition by means of other particles obtained by the pseudopodia from the surrounding medium is by no means excluded; indeed it may be regarded as certain that numerous Radiolaria (especially such as contain no symbiotic Algoid cells) are nourished for the most part or exclusively by this means. Diatoms, Infusoria, Thalamophora (Foraminifera) as well as decaying particles of animal and vegetable tissues can be seized directly by the pseudopodia and conveyed either to the sarcodictyum (on the surface of the calymma) or to the sarcomatrix (on the surface of the central capsule) in order to undergo digestion there. The indigestible constituents (siliceous shells of Diatoms and Tintinnoidea, calcareous shells of small Monothalamia and Polythalamia, &c.) are here collected often in large numbers and removed by the streaming of the protoplasm.