INFUSORIA. 69 



tlie process of separation first commences in the 

 nucleus, but this is incorrect, since in some cases 

 its division into two parts is not effected until 

 that of the body is nearly complete, or it may 

 happen that fission of the nucleus is not partici- 

 pated in by the body as a whole. 



h. Geniination (or the development of buds) 

 takes place far less frequently than fission. It is 

 best seen in Vorticella. Here a bud is formed 

 (usually near the posterior extremity of the bod}^) 

 by the expansion of a portion of the cortical layer. 

 This at first derives its nutriment by means of a 

 diverticulum or prolongation proceeding from the 

 digestive cavity of the parent animal. At length 

 this connection is interrupted, the bud becomes 

 furnished with a posterior circlet of cilia, by the 

 aid of which it finally detaches itself and S"v\T[ms 

 freely about in the surrounding water {fig. 1 2, 3). 

 It should, however, be borne in mind that the dif- 

 ference between fission and gemmation is more 

 apparent than real, and in many cases it is im- 

 possible to distinguish the one from the other. 



c. Some Infusoria, previously to undergoing fis- 

 sion, become coated with a secretion of gelatinous 

 matter which gradually hardens so as to enclose 

 the body in a ^cyst.' In other cases, peculiar 

 vesicular bodies become formed in the interior of 

 such cysts, through which they finally burst, and, 

 becoming ruptured at the apex, give exit to the 

 embryos contained in their interior. But it would 

 appear, from recent observations, that the pre- 

 vious formation of a cyst is by no means necessa- 

 rily antecedent to the production of the vesicles 

 in question. 



According to Stein, the process of encystation 



F 3 



