THE INFUSORIA. lOl 



conjugation takes place by the complete and permanent 

 fusion of two individuals, which are sometimes of equal 

 dimensions ; though, in other cases, one is much smaller than 

 the other, and, while it is in course of absorption, looks like a 

 bud, and was formerly taken for such (Fig. 9, A, g^ h). The 

 small individuals usually take their origin from a group of 

 small stalked Vorticelloe^ which are produced by the repeat- 

 ed longitudinal division of a Vorticella of the ordinary size. 

 The result of the conjugative act is that the " nuclei " of the 

 two individuals, either before or after their coalescence, 

 break up into a number of segments. The segments may 

 remain separate, or coalesce into a single mass, called by 

 '^iein placenta. In the former case, some of the segments 

 become germ-masses, while the others reunite to form a new 

 " nucleus ; " in the latter, the placenta throws out a number 

 of germ-masses, and then assumes the form of an ordinary 

 *' nucleus." The germ-masses give off portions of their sub- 

 stance, including part of their " nucleus," and these become 

 converted into ciliated embrj^os, which escape by a special 

 opening. Knobbed tentacles, like those of the Acmet<x, 

 have not been observed in the embryos of the Peritricha, 

 nor has their development been traced out. 



If the bodies regarded as acinetiform embryos of the 

 Ciliata are really such, they may be taken to represent the 

 myxopod stage of the Catallacta^ and the relations of the 

 Achiitm to the Ciliata would appear to be that they are 

 modifications of a common type, differing from the Catal 

 lacta in having tentacula instead of ordinary pseudopodia. 

 In the Acinetce, the tentaculate stage is the more permanent, 

 the ciliated stage transitory ; while, in the Ciliata^ the cili- 

 ated stage is the more permanent, and the tentaculate stage 

 transitory. 



