144 ARTIFICIAL PARTHENOGENESIS [CH. 



To sum up, then, it may be concluded that the formation 

 of the fertilisation membrane is due to a cytolytic action 

 on the surface layer of the egg, and that a further effect of 

 this action is to induce nuclear and cell-division, but that 

 in many cases when once this cytolytic action has begun, it 

 tends to continue, probably through want of regulation of 

 the oxygen absorption, and to lead to complete disintegra- 

 tion. If, however, the excessive oxidation can be inhibited 

 until the egg has restored its power of regulation, the cell- 

 division that has been started will continue, and the egg 

 will develop into a normal larva, which, as experiment has 

 shown, may undergo metamorphosis and grow into a fully 

 developed urchin. 



This conclusion suggests a number of interesting en- 

 quiries, especially with regard to the nature of fertilisation 

 by the spermatozoon and of the stimuli which lead to cell- 

 division. To pursue these at all fully would lead into some- 

 what abstruse questions with regard to the physico-chemical 

 condition of protoplasm, its permeability to electrolytes, 

 and the nature of the chemical processes which take place 

 in its metabolism. Work on these subjects is as yet only in 

 its infancy, and it promises to lead to some of the most 

 fundamental results which biological enquiry can ever hope 

 to reach. In the present short sketch of the subject, how- 

 ever, only some of the more superficial aspects of the 

 problem can be touched. 



LOEB comes to the conclusion that the development of 

 the egg when fertilised by a spermatozoon is due to the 

 introduction of a cytolytic agent by the sperm, which 

 alters the stability of the egg surface, so causing the pro- 

 duction of a fertilisation membrane, and that destructive 

 cytolysis is prevented by the presence of a second substance 

 which inhibits any further cytolytic action. This idea is 



