656 SYSTEMATIC HISTOEY OF THE INFrSORIA. 



the microscope, aroiind which objects they play after the fashion of their 

 freshwater allies. In the ocean we have few or no counterparts of the 

 stagnant pools found on land ; those dark holes on rocky coasts, the homes of 

 the Actinice and the seaweeds, which would otherwise represent ponds and 

 ditches, are too constantly distui'bed by the tidal wave to admit of the accu- 

 mulations of decaying vegetation so favourable to the existence of the fresh- 

 water species. 



Classification". — The exact place which the Rotatoria should occupy in 

 the zoological scale is as yet undetermined, since discordant opinions are 

 entertained on the subject by some of our most eminent naturalists, as will 

 be seen by a recurrence to Part I. of this work (p. 392). The question can 

 be decided only by a careful study of their development as compared with that 

 of other animals. Most inferior creatures are the permanent representatives 

 of conditions which are merely transitional in the advance from the ovum to 

 matmity of some higher form, — the former beings obviously occupying a posi- 

 tion subordinate to the latter, inasmuch as they never advance beyond a state 

 which only occiu'S in the higher animal in its immature and imperfect con- 

 dition. The Myriapod and the Worm, with theii^ strongly-marked vegetative 

 repetitions of parts, obviously find a temporary representative in the crawling 

 caterpillar, but not in the fully-formed winged insect of which the caterpillar 

 is but the rudimentary larva. Consequently the Worm and the Myriapod 

 must alike be placed below the Insect, if we arrange animal forms in a linear 

 series according to their development. Supposing this method of ascertaining 

 the true zoological position of any class of animals to be correct, the question 

 naturally arises, what larval states of other animals are most closely repre- 

 sented by the permanent forms of the Rotifera ? It is clear that the Eotifera 

 have little afiinity with the Polygastric Infusoria ; for, though the family of 

 Yorticellina amongst the latter animals seems to constitute a sort of inos- 

 culating link, the affinity of the VorticeUce to the Rotatoria appears to be 

 rather one of resemblance than of relationship. The history of the VorticeUce^ 

 as worked out by Professor Stein, reveals morphological changes wholly dis- 

 similar from what occurs in the Rotatoria, amongst which the encysting- 

 process, so characteristic of the VorticeUce-, has no place. This process is 

 obviously one of the phenomena of development by gemmation which is most 

 prevalent amongst the lower animal forms, and becomes less frequent as we 

 ascend, until, amongst the higher classes, it never occurs. In ascertaining the 

 relation of the Rotatoria to the VorticeUce,, it is necessary to inquii'e how far 

 this reproduction by gemmation, as distinct from sexual reproduction, has 

 any existence amongst the former animals ; and this is precisely the question 

 which we are as yet unable to answer. It has been suggested that, of the 

 two forms of eggs known to be produced by some Rotatoria, one group con- 

 sists merely of buds encased in a shell, whilst the others are the tnie sexual 

 products ; but such eminent observers as Professor Huxley and Dr. Cohn are 

 at issue as to which of the two kinds of ova are to be respectively regarded 

 as true eggs or as gemmae. Dr. Cohn contends that the bodies ordinarily 

 regarded as eggs are merely gemmae thrown off fi*om the organ believed to 

 be an ovary, \\athout any fertilization by a male animal, — thus accounting 

 for the extraordinary profusion in which these eggs are developed, whilst so 

 many observers have been baffled in their attempts to discover spermatozoa 

 or any male organization. The mode of development which Professor Huxley 

 observed in the ova of Lacinularia, and Professor Williamson in those of 

 Melicerta, are not incompatible with the idea of their being gemmae, and 

 the ovary a gemmiferous stolon. Supposing all this to be true, we have, 

 in the formation of those shelled gommoc, an analogue to the development of 



