AND THE LOWER ANIMALS. 163 



This is, as it were, the history of a butterfly's egg, 

 from which sprung a chrysalis capable of producing, 

 by internal gemmation, first several generations of 

 beings like itself, and then a certain number of butter- 

 flies. Here, then, are several generations of scolex; 

 the strobila stage, as in the preceding cases, is 

 wanting, and the proglottis is sometimes, even during 

 its whole lifetime, like the scolex,* but at others 

 differs from it in certain particulars already re- 

 ferred to. 



This analogy between the external forms of the 

 scolex and proglottis in the same species, renders 

 it occasionally difficult to distinguish between the 

 various phases of geneagenesis, and, as it were, masks 

 the phenomenon. The process is more clearly seen 

 among the biphorse, where the physiological laws are 

 in some measure indicated by the existence of per- 

 ceptible characters. 



This subject has been investigated by many natural- 



the " Zeitsclirift fur wissenschaftliche Zoologie," 1850, on the earlier 

 phenomena of development, was led to confound, so to speak, 

 reproduction by ova with reproduction by fully-formed individuals. 

 His view was opposed more or less clearly by Siebold, Owen, 

 V. Carus, and Dr. Burnet, and in a more direct manner by Lub- 

 bock " On the Double Method of Eeproduction in Daphnia" — Philo- 

 sophical Transactions, 1857, — and Leuckart, " Zur Kenntniss des 

 Generationwechsels und der Parthenogenesis bei den Insecten ; " 

 Moleschott's " Untersuchungen," 1858. Professor Huxley's admir- 

 able memoir " On the Agamic Eeproduction and Morphology of 

 Aphis" — Transactions of the Linnean Society, 1858, — in which he 

 has not only summed up, but completed all the preceding researches, 

 leaves this subject settled beyond doubt. We shall discuss all 

 these questions further on. 



* Bonnet has observed wingless individuals which performed 

 the same functions as those with wings, and gave unequivocal 

 proofs of sexuality. 



M 2 



