386 THE WONDER OF LIFE 



reared tadpoles by this aspermic development, and he was 

 thrice successful in reaching the stage of miniature frogs. 

 It is interesting to find that the nuclei were smaller than 

 the normal, and Levy believes that they had only half the 

 normal number of chromosomes. 



The experiments in question illustrate very clearly that, 

 as we have indicated, several quite distinct things take 

 place in ordinary fertilization. The entrance of the sper- 

 matozoon implies some degree of mingling of the paternal 

 with the maternal inheritance, and it also implies some 

 stimulus to cleavage or the removal of some hindrance. 

 In the artificial parthenogenesis effected by MM . Bataillon 

 and Henneguy the role of sperm- stimulus was discharged 

 by a needle, and the inheritance remained, of course, purely 

 maternal, for there cannot be a hybrid between a needle 

 and a frog. As a French writer puts it : ' il ne peut etre 

 question d'heredite du cote du pere, car on ne voit pas 

 tres bien les jeunes grenouilles heritant des proprietes de 

 leur epingle paternelle '. While some incline to think 

 that the spermatozoon introduces a stimulus, perhaps of 

 the nature of a ferment, Loeb has suggested that 

 the spermatozoon may remove ' a negative catalyser or 

 condition ', the presence of which somehow keeps the 

 ovum from developing. The stimulus may be the removal 

 of an inhibitory influence. Further experiments are re- 

 quired before this question can be securely answered. 



We have seen that a quite ripe ovum has in its nucleus 

 half the normal number of chromosomes ; if this ovum be 

 artificially stimulated to development, the cells of the 

 young animal should also contain only half the normal 

 number. According to Dehorne, this was the case 

 in an eight days' old frog-tadpole, reared from an 



