Jan. 17, 1884J 



NATURE 



275 



for the systematic distinction of the orders, and is, moreover, 

 subject to various exceptions. 



Among the new Uadiolaria of the groups above mentioned 

 (Hscovered in the Chalhngc-r collection, there were, moreover, 

 mouozox and polyzoic species whicli correspond completely, 

 even in the specific characteristics of the skeletal form. For 

 c-vample, a monozoic Thalassoxanihium has precisely the same 

 characteristic spicules as the common cosmopolitan Sfhu:rozaum 

 functaium, but whilst in the latter the small polyzoic central 

 capsule incloses a large central oil globule and numerous small 

 peripheric nuclei, in the former the central capsule, w hich is three 

 times as large, incloses a single, large central nucleus and nume- 

 rous small peripheric oil globules. The complete identity of 

 the characteristic skeletal form might even lead us to sup- 

 pose that a kind of alternation of generation may take place 

 between the tw'o f^irms. In the same «ay, a social Collosphara 

 corresponds completely to a solitary Cenosphara, the polyzoic 

 Airospkara to the monozoic Conosphicia, and so forth. 



On the ground of these observations — the importance of which 

 I shall explain in detail in my work on the Challenger Kadio- 

 laria — I consider the distinction between monozoic and polyzoic 

 Kadiolarians (which I contrasted in 1862, according to Miiller, as 

 Monocytlaria and Pol 1 cyttaria) as practically unimportant, and 

 for the present connect the polyzoic families in the system imme- 

 diately with the monozoic. In this way the number of the six 

 <.>r seven groups is reduced to four, as I refer all the groups thus 

 formed to Hertwisj's Peripylea. As I have already shown (1S81, 

 I.e. p. 421), these may be again divided in pairs into two principal 

 groups or sub-classes — into Holotiypiuta and Merotrypasta. The 

 Holotrypasta (Acuiitharia and Peripylea, the latter including the 

 Collodaria, Symbelaria, and Syncollaria] includes all Radiolaria 

 in which the capsule membrane is pierced on all sides by fine 

 pores, and the pseudopodia consequently radiate equally on all 

 sides. The Merotrypasta (Monopylaria and PluTodaiia) include 

 all those Radiolaria in which the membrane is pierced at one 

 side either by a single area of pores or by openings confined to 

 a few spots, so that the pseudopodia project from the central 

 capsule as a single bunch or as slightly separated bunches. 



The high standard importance of the central capsule for the 

 proper conception of tlie Radiolaria to which I first drew atten- 

 tion in my monograph, 1S62, has since been recognised by 

 Hertwig and most other investigators of these Protista, but 

 recently disputed by Carl Brandt (Moiiatsb. Berlin. Akad. 18S1, 

 p. 391). As I reserve the detailed reasons for my opinion for 

 my work on the Challenger Radiolaria, I shall now merely re- 

 mark that my more recent researches have fully corroborated 

 my former views, and that in all true Radiolaria the central 

 capsule is separated by a distinct membrane from the extra- 

 capsularium (or external gelatinous soft part). The so-called 

 ' ' freshwater " Radiolaria {\\ hich, from'absence of the membrane, 

 are not Radiolaria but Helizoa) do not of course furnish any 

 counter-proof. Brandt's erroneous assertion rests upon the ex- 

 tremely limited amount of material inve^tigated by him. Care- 

 ful investigation enabled me to discover the capsule, even in all 

 sjJecies which he regards as "without capsule." In isolated 

 species, however, the capsule membrane is somewhat late in 

 forming a definite boundary between the capsule and the gela- 

 tinous sheath (sometimes just before the formation of spores), 

 whilst in other cases it usually takes places at a very early stage. 

 I therefore maintain now, as formerly, that the chief character 

 of the class is the differentiation of the unicellular body into two 

 essential, principal component parts, viz. the inner central cap- 

 sule with nucleus and membrane, and the outer gelatinous sheath 

 w ith matrix and forest of pseudopodia. On the other hand, it 

 is immaterial whether " yellow cells " (or " zooxanthella ") are 

 present or not. I found them wanting in many cases, though 

 they are usually jiresent. I therefore agree with Cienkorosky, 

 and regard the symbiosis of these unicellular Algae as an acci- 

 dental and not an essential phenomenon. They are in no way 

 riecessary for the nourishment of the Radiolaria, though they 

 may be important agents in the matter. 



Meantime I am convinced that the four orders of the class 

 Radiolaria, .^ran//M;rW, Spiimellaria, N'assellaria, and Phceodaria 

 rejiresent four distinct, perfectly natural, principal divi-ions. In 

 each of these four orders the numerous forms belonging to it, 

 despite their astonishing variety, may be referred by morpholo- 

 gical comparison to a common primitive form, w hich may there- 

 fore be regarded as their ancestral form in a phylngenetic sense. 

 Tliis iihylo^rpn^tic view of the four orders ns distinct monophy- 

 leiic groups IS justified by the fact that the remaikable and ex- 



tremely complicated relations of all the forms of each common 

 ancestral group have the .=ame natural, strong phylogenetic sig- 

 nification as they have in the comparative anatomy of the Verte- 

 brata or of the Articulata. Biitschli was therefore in the right 

 at the close of his admirable dissertation on the skeletons of the 

 Cyrtida (1S81, I.e. p. 538), where he lays stress on the fact that 

 the complicated phylogenesis of this section, so rich in specific 

 forms, may be regarded as an excellent argument in favour of 

 the doctrine of descent, and that in this way those pains- 

 taking investigations of the microscopic, world (which many 

 "exact physiologists" consider mere morphological trifling) 

 come to be of real importance. 



I. The Acantharia, which are distingui-hed from the three 

 other orders by their organic acanthine skeleton — they never 

 have a true siliceous skeleton — correspond on the whole to the 

 Aeanthonielree of J. Miiller (including, however, part of the 

 Haliomma), and to the Acanthometrees of Hertwig, which he 

 divides into Aeanthometrida and Aeanthophraetida. I hold the 

 remarkable Aetinelius to be the ancestral f >rm of this order. It 

 was first described by me in 1865, but I have lately found seve- 

 ral forms closely allied to it, partly Astrolophida, partly Litho- 

 lophida, in the Challenger collection. In Aetinelius the spheri- 

 cal central capsule is pierced by numerous simple, radial spicules 

 (without definite numljer and arrangement) meeting in the centre 

 of the capsule. Aetinelius may be held to have arisen inmie- 

 diately from Aetinosphariuni by the hardening of the firmer axial 

 fibres in the radial pseudopodia of the latter into radial spicules. 

 Aetinelius is the common ancestral form, on the one hand, of 

 the whole Aetinehdir (Astrolophida and Litholophida), all with 

 indefinite number and arrangement of the spicules, and, on the 

 other hand, of the remaining Aeanthatia, in which twenty 

 radial spicules are invariably arranged acc.jrding to J. Midler's 

 law in five four-rayed zones. The oldest of these are the Acan- 

 thonida (or Acanthometra in the more limited sense) from which 

 the Dorataspida and Diploconida having shells are derived later 



II. The Spumellaria, by which I understand Hertwig's Peri- 

 pylea, Thalassicollea, and Sphiirozoea, had been previously united 

 with tolerable accuracy by Ehrenberg, on the ground of observa- 

 tions made by him on the skeletons of the fossil Radiolaria of 

 the Barbadoes, and opposed to the Nassellaria as Polydictya or 

 Polycystina eomposita. His Spyridina (our Spyroida) belongs, 

 ho.vever, to the latter, not to the former. All Spumellaria 

 (which may also ultimately be termed Peri])ylaria or Peripylea) 

 have — in contradistinction to the Nassellaria and rhreodaria — a 

 central capsule pierced on all sides by fine pores, and agree in 

 this respect with the Acantharia, from which, however, they 

 are distinguished by the absence of the acanthine skeleton. All 

 Spumellaria may be easily referred to a common ancestral form 

 — to Actissa, the simplest: form of the ThalassicoUida. An in- 

 teresting species belonging to Aetissa w as accurately described 

 by HerH\'ig in 1S70, under the name Thalassolampe primordialis 

 (" Organismus," p. 32, taf. iii. fig. 5). It has neither the extra- 

 capsular alveola of Thalassolampe nor the intracapsular alveola 

 of Thalassicolla. I observed another species of the genus, which 

 I shall describe later in detail, as Aetissa princeps in Ceylon, 

 1S81. ^r/iVj-a certainly represents the simplest possible Radio- 

 larian form, in a mea-ure the actual embodiment of the simplest 

 ideal type of this wholeRhizopod class. In a phylogenetic sense it 

 may therefore claim to be regarded as the ancestral form not 

 only of all Spumellaria, but perhaps also of all Radiolaria. All 

 Collodaria (ihe solitary ThalassicoUida and Thalassosphajrida, the 

 social CoUozoida and Sphasrozoida) are derived immediately 

 from it, then all Sphierellaria. The ancestral group of the 

 latter section, which is richest of all in specific forms, is the 

 Spheroida (or Spharida], and, first among them, the Mono- 

 sphserida, furnished with a simple, fenestrated spherical shell. 

 From the latter all the others, viz. Pylonida, Zygastida, Discoida, 

 and Lithelida, can be derived without difficulty. 



III. The Nassellaria, which correspond on the whole to 

 Hertwig's Monopylea, had already been defined by Ehrenberg as 

 Monodyeta or Polycystina solitaria, in contrast to his Spumellaria. 

 His definition was correct on the whole, though the Spyridina 

 (our Spyroida), which he places among the latter, belong rather 

 to the former. Hertwig was the first to determine correctly the 

 essential characters of this large order, so wonderfully rich in 

 forms, viz. the simple area of pores at one pole of the capsule 



I axis, 1879 {I.e.), and I would therefore have retained his name, 



I Monopylea or Monopylaria, for the entire order, had it not been 



equally suitable to jiart of the Phseodaria. I therefore prefer 



