CHAP, iv.] 



OF ANIMAL GENERATION. 



323 



i invertebrates are provided with the genital apparatus of the two 

 i sexes ; but these apparatus are so arranged that autofecundation 

 is almost impossible. 



Sometimes, however, especially in the bivalvous mollusks, for 

 j the most part fixed and immovable, there is autofecundatory 

 hermaphrodi sm. 



On the whole, a general fact results from the examination 

 of generation among the inferior animals, the great diversity 

 of processes, and also a sort of confusion in their employment. 

 The species are still ill differentiated ; there is in the plan ofc 

 their organism a sort of indecision. Nature, to use the language 

 of Darwin and of many others, seems to hesitate, to grope ; she 

 has not yet found the best way, and tries all ways simulta- 

 neously. But when the sexuality is well marked, when there is 

 formation of a male cell and a female cell, the primary acts of 

 reproduction and fecundation assume an almost uniform character. 

 In all animals, the female cell, the ovulum, is nearly identical. 

 At first the ovulum differs in nothing from an ordinary cell, if 

 we do not allow ourselves to be led astray by the special names 

 invented by the embryologists. The 

 complete ovulum is composed in effect of 

 an enveloping membrane, the vitelline mem- 

 brane, or zona pellucida, of a content or 

 protoplasm, the vitellus, of a nucleus or 



, . 7 p 11 



germinative vesicle, or a nucleole or germi- 

 native spot (Fig. 47). 



According to M. Van Beneden, there FIG. 47. 



are in the ovulum an accessory part and ovulum of woman magnified 



, . -i mi , i-ii 250 times : a. pellucid zone ; 



an essential part. The last, which he &, vitellus ; c, germinative 

 calls cell-ovum, has in all the animal Sative^^ ** ger " 

 kingdom an identical evolution, and 



is represented solely by the nucleus of the ovulum, by the 

 germinative vesicle, and a small part of the vitellus which sur- 

 rounds it. 1 It is certain, at all events, that the germinative 

 1 Cl. Bernard, loc. tit. 



Y 2 



