ARTIKIOTAL I'AllTHENOnENESIS AND FERTILISATION. 508 



all there is only a formal difference, for the finiclamental 

 problem is the same when the question is raised how the 

 centrosome exercises its activities. 



Loeb (1901), on the physico-chemical side, suggests that a 

 catalytic substance is carried by the spermatozoon into the 

 egg, that is one which accelerates physical or chemical 

 processes which would occur without it. The K ions act as 

 catalysers, and the loss of water acts also, though less 

 directly, in the same way, and it may be that it gives rise to 

 substances which act catalytically. Inasmuch as in Chgetop- 

 terus the normal development does not show the character- 

 istics of a treatment of the eggs by K, it is probable that 

 normal fertilisation is not brought about by K ions. 



Delage (1901) considers that the egg is in an nnstable 

 state of equilibrium, which is readily upset by various 

 agencies — loss of water, heat, etc., and he lays some weight 

 on the specific action of the salts. He finds that the 

 chloride of manganese has, for Asterias, a specific action 

 superior to that of the alkaline salts. Together with his son, 

 he showed that in the case of the sea-ui*chin there was less 

 magnesium chloride in the sperm than in the eggs, by about 

 1 per cent., so that this salt could not have a specific action. 



Among other possible factors in the action of the sperma- 

 tozoon, he gives prominence to its abstraction of water from 

 the cytoplasm. During maturation the nuclear sap is shed 

 into the cytoplasm ; until this is effected by the solution of 

 the nuclear membrane, fertilisation is not possible ; it is just 

 at this " critical stage" in Asterias that he finds artificial 

 parthenogenesis most liable to occur. In the specialisation 

 of the sexual elements, the egg thus becomes rich, while the 

 spermatozoon has become poor, in v^^ater. After the sperm 

 head has entered the ovum it increases in size by abstraction 

 of fluid from the egg protoplasm, and this abstraction of 

 water by the sperm nucleus has to be reckoned with as a 

 possible factor in fertilisation. 



Apart from the large assumptions involved in such an 

 hypothesis, the facts of " partial fertilisation, and the local- 



VOL. 40, PART 3. — NEW SERIES. I J 



