OF THE ROTATOHIA, 447 



riurn, foiu' or five ova sometimes so completely develope themselves, that the 

 young creep out of theii' envelopes, in which they vrere coiled up in a spii^al 

 manner, extend themselves, and put their wheels into motion while within 

 it ; and they sometimes occuj^y two-thii'ds of the bulk of the parent. So 

 Mr. Gosse tells us that in AsjpJanclma '' the o^Tim produces the living young 

 in the ovisac, which, when matured, occui)ies the whole lower part of the 

 parent." The occuiTcnce of embryos free within the saccular ovary of Ste- 

 phaiioceros (and still more, if as some have thought, they detected them loose 

 in the general cavity of the body) forms another bond of affinity between this 

 aberrant genus of Eotatoria and the Bryozoa. Where the young in general 

 quit the parent in a free, and so far perfect form as to be able to lead at 

 once an independent existence, the animals may be said to be viviparous 

 (producers of li^-ing yoimg). This viviparousness (viviparity) is still more 

 pronounced in some Philodincea and in Alhertia, in which the formation of 

 an actual egg-shell seems to be omitted, and the developed embryo to be at 

 once Hberated within the sac of the ovary, where it may be seen in active 

 movement. 



The Embryo Metamorphosis. — It has already been remarked, generally, 

 that the embryo on emerging from the e^^ has all the characters of its class, 

 and is complete in its internal organization ; that any dissimilarity between 

 the new-born and the adult animal is due, not to the absence of parts or 

 organs, but to their lesser growth and their imperfect expansion or evolution. 

 In other words, the Rotatoria undergo no positive metamorphosis ; they j^ass 

 thi'ough no intermediate phases of existence, no larval form resembhng that 

 of any Protozoa, in advancing from the embryonic to the complete and per- 

 fect condition. 



Leydig does not partake this opinion, but thinks that a metamoriDhosis is 

 exhibited in the course of development of most or all Eotatoria, certainly not 

 complete, but still sufficient to advance it as a phenomenon of the class. He 

 specially adduces the instance of the embiyo of Stephanoceros, as the most 

 striking proof (XXXYII. 3, 4), and he adds that, if the representation by 

 Ehrenberg of the young of Triarthra Jongiseta be correct, the fact of a meta- 

 morphosis must be recognized also in that genus. Again, he notes the great 

 difference between the newly-bom and the adult animals in several genera, 

 e. g. in Tuhicolaria and Melicerta, where the cihary wi^eath is still very 

 simple, and the absence of the tentacles (antennaD) sufficiently notable 

 (XXXYII. 15) to render the subsequent modifications an act of metamor- 

 phosis. Moreover, the disappearance of the bunch of ciha in the young state 

 at the end of the pseudopodium, and lilvewise that of the coloui^ed eye-specks 

 in many genera, when the adult condition is attained, are also indications of 

 the same phenomenon. 



The advocacy of this opinion was especially incumbent upon Leydig, in 

 order to furnish an additional argument in favour of the affinity of the Eota- 

 toria with the Crustacea. But even w^re the evidences of metamorphosis 

 among the Eotifera as complete as he represents, they would serve his pur- 

 pose, of demonstrating the affinity he advocates, but Httle, seeing that the 

 immature Eotatoria have no real resemblance to the larval Crustaceans with 

 their three pairs of jointed feet. Cohn (Siebold's Zeitschr. 1855, p. 481) has 

 discussed this question, and surmises that the peculiar embryo of Stephano- 

 ceros, which Leydig cites as the strongest instance of an act of metamor- 

 phosis, is a male being (XXXYII. 3). As to the other supposed instances, 

 Cohn disproves its occurrence in Brachionus, and considers the disappearance 

 of the eye-speck in Tuhicolaria and Melicerta too trivial a circumstance to 

 urge in its support. 



