322 BIOLOGY. [BOOK iv. 



Internal gemmiparity, endogenesis, is observable in the olvoces, 

 the acephalocystes, and so on. The cavity of the animal fills 

 itself with vesicular animals similar to the mother vesicle. 

 Certain of these newcomers, those the most developed, contain 

 themselves other individuals, which in their turn contain others ; 

 so that three generations are thus inclosed one within the 

 other. 



According to M. Balbiani many fissiparous or gemmiparous 

 species are at the same time capable of sexuality, but of an 

 alternant sexuality. 1 In the green paramecium (Paramecium 

 bursaria) the sexuate cells pre-exist ; they enlarge at a given 

 moment. In the largest of these cells ovula with a nucleus and 

 a nucleole are formed. In the smallest the intercellular sub- 

 stance divides into small bacilla, which are spermatozoaries 

 charged with fecundation. 



This hermaphrodite sexuality enters into action at a determi- 

 nate epoch. The scissiparous process would exhaust itself little by 

 little, would end by no longer producing any but puny, imperfect 

 individuals, and would lead to absolute sterility, if sexuality did 

 not come to give to the reproductive property a new vigour. 



The lowest mode of sexual reproduction, conjugation, i 

 observable in the colpods. Two individuals unite, encyst them- 

 selves, and blend into one common mass. Then this common 

 mass reproduces by fractionment new individuals. 



The mode of copulation of the green paramecium recalls still, 

 though faintly, conjugation. In its sexual phase, each para- 

 mecium is provided with reproductory bodies male and female, 

 as we have recently seen ; but nevertheless, a thing, however, 

 frequent among the hermaphrodites, the fecundation is mutual. 

 Two individuals juxtapose themselves mouth to mouth during a 

 duration of many days, and they exchange their spermatozoids. 

 It is an example of the horror which Nature has of autofecun- 

 dation, to use Darwin's expression. Many hermaphroditical 



1 Balbiani, Sur T Existence d'une Generation Sexuelle chez les Infusoires 

 (Comptes Jtendus de I'Academie des Sciences, t. XLVI). 



