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NA TURE 



\yune 9, 1887 



there are very many species which are known only from 

 one locaHty, and probably many small local faunas exist, 

 characterised by the special development of particular 

 groups. From the very richness of the material, Prof. 

 Haeckel has found it impossible to work out completely 

 the local distribution of all the species. 



From the tropics the abundance of species seems to 

 diminish regularly towards the Poles, and more rapidly in 

 the northern than in the southern hemisphere ; the latter 

 also appears to possess more species than the former: a 

 limit to Radiolarian life towards the Poles has not yet been 

 found. The greater abundance of Radiolaria in the 

 tropical seas is to be accounted for by the more favour- 

 able conditions of existence, rather than by any difference 

 in temperature. One station (271) of the Challenger 

 Expedition, situated almost on the Equator, in the Mid- 

 Pacific, exceeds all other parts of the world hitherto 

 known in respect of its wealth of these forms ; and more 

 than 100 new species are described from it. The fauna of 

 the Pacific Ocean exceeds that of both the Indian and 

 Atlantic, but the fauna of the Indian Ocean is that least 

 known. 



In reference to the bathymetrical distribution, it seems 

 certain that numerous species of this class are found 

 at the most various depths of the sea, and that certain 

 species are limited to particular vertical zones, and are 

 adapted to the conditions which obtain there. In this 

 respect three different Radiolarian faunas may be distin- 

 guished — the " pelagic," " zonarial," and " abyssal." More 

 than half of all the species known as recent belong to the 

 last fauna. 



The chapter on the geological distribution is full of 

 interest. Radiolaria are found fossil in all the more im- 

 portant groups of the sedimentary rocks of the earth's 

 crust. Whilst a few years ago their well-preserved sili- 

 ceous skeletons were only known in considerable quantity 

 from Tertiary marls, very many are now known to occur 

 in Mesozoic, and a few in Palaeozoic, strata. By the aid of 

 improved modern methods of research, it has been shown 

 that many hard siliceous minerals, especially cryptocrys- 

 talline quartz, contain numerous well-preserved Radio- 

 laria, and sometimes these are composed almost entirely 

 of closely compacted masses of such siliceous shells. 

 The Jurassic quartzes (Switzerland), as well as the Ter- 

 tiary marls (Barbados) and clays (Nicobar Islands), may 

 be regarded as " fossil Radiolarian ooze " ; and, since speci- 

 mens have also recently been found both in Silurian and 

 Cambrian strata, it may be inferred that Radiolaria are 

 to be found in all fossiliferous sedimentary deposits, from 

 the oldest to those of the present day. Among the Mio- 

 cene Radiolaria, numerous species are not to be distin- 

 guished from the corresponding still living forms. On the 

 other hand, those genera which are rich both in species 

 and individuals (recent as well as fossil) present continu- 

 ous series of forms which lead gradually and uninterrupt- 

 edly from old Tertiary species to others still living, which 

 are specifically indistinguishable from them. 



As Chapter XI. of the introductory portion of the 

 Report, Prof. Haeckel gives a very valuable account of 

 the progress of our knowledge of the Radiolaria from 

 1862 to 1885. In his earlier monograph he had already 

 given a critical discussion of the works which had 

 appeared prior to 1862 : we find here a full list of the 



publications from 1834 to 1884, in which list a little of the 

 author's old trenchant style of criticism breaks out ; for 

 he has heaped together in an appendix, to which he gives 

 a somewhat needlessly offensive name, "all the absolutely 

 worthless literature, which contains either only long- 

 known facts or false statements, and which may therefore 

 be entirely neglected with advantage." While we would 

 not, for all the Radiolaria in the sea, give the list of this 

 "foul" literature, we may relieve the reader's mind by at 

 once mentioning that the name of Ehrenberg does not 

 appear in it, and that the value of the laborious works ot 

 the great but too self-reliant German in this field meets 

 with all proper appreciation. 



The unicellular nature of the Radiolaria was first esta- 

 blished by Richard Hertwig in 1879, and was brought by 

 him into conformity with our present histiological know- 

 ledge and the new reform of the cell-theory. Huxley, 

 who was the first to examine living Radiolaria with any 

 accuracy, declared, so long ago as 1851, that Thalassi- 

 colla nucleafa was a unicellular Protozoon. Later, both 

 Johannes Miiller (1858) and Haeckel (1862), recognising 

 the peculiar " yellow cells " which occur in many. Radio- 

 laria, in large numbers, as true nucleated cells, thought 

 it impossible to maintain this view ; and it was not until 

 Cienkowski (1871) and Brandt (1881) had shown that 

 these " yellow cells " did not form part of the Radio- 

 larian structures, but are symbiotic unicellular Algae, that 

 it was possible to revive and demonstrate anew the uni- 

 cellular nature of the Radiolaria. 



From a morphological stand-point the individuality of 

 the unicellular elementary organism is obvious in the 

 solitary Radiolaria (Monobia) ; and the whole body with 

 all its constituent parts, and not merely the central 

 capsule, is to be looked on as a cell. But this unicellular 

 organisation must be noted as differing from that of all 

 other Protista, inasmuch as an internal membrane (capsule 

 membrane) separates a central from a peripheral portion. 



The membrane of the central capsule is invariably pre- 

 sent at one period or another of the life of the organism. 

 Karl Brandt, indeed, has recently stated that in some 

 forms it is absent ; but Haeckel has recognised its pre- 

 sence in over one thousand species, and even in some ot 

 those in which Brandt was unable to find it. It is often 

 very delicate and may easily be overlooked, though the 

 application of the proper reagents will renc'er it always 

 discernible. Those Radiolaria in which for a time it is 

 absent are young of species in which the membrane is only 

 formed immediately before sporification, and persists but 

 for a short time. 



All Radiolaria possess a nucleus, but they present two 

 different conditions in respect of its behaviour, since in 

 their young stages they are uninuclear, and in later stages 

 they are multinuclear. Before the formation of swarm- 

 spores the nucleus divides into many nucleoli. Thus the 

 nucleus is pre-eminently the organ of reproduction and 

 inheritance. The division of the originally single nucleus 

 into many small nuclei may take place at very different 

 periods, so that Haeckel divides the Radiolaria into the 

 "precocious" and the "serotinous." Into the subject of 

 the skeleton formation and that of phylogeny the space at 

 our command will not allow us to enter ; it will suffice 

 to say that they are treated at great length and with 

 consummate skill. 



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