AUTO-PARTHENOGENESIS IN ARBACIA AND ASTERIAS. 405 



of the surface film or cortical layer, lipoid solvents, and even the 

 prick of a needle having been found effective. These methods, 

 each of which is capable of variation and modification, have 

 nothing in common except their result, and it is idle to try to 

 imagine any direct causal connection between them and the 

 result. However one effect, common to all, seems to stand inter- 

 mediate between the parthenogenetic result, and the experi- 

 mental means used to induce it. This common intermediary 

 is a change in the permeability of the surface of the eggs, and in 

 the experiment in which parthenogenesis is induced in one ovum 

 by the secretion of another it is not necessary to assume that 

 anything occurs that does not also take place in all the other 

 cases. The same reasoning applies also to auto-parthenogenesis, 

 a process which was found by application of the surface-alteration 

 theory, and in total ignorance of the fertilizin hypothesis. 



Now the picture of fertilization with sperm given by the fertil- 

 izin theory is briefly the sperm-receptor-amboceptor-egg-re- 

 ceptor reaction. In the picture of auto-parthenogenesis, the 

 sperm is dropped, leaving the amboceptor-egg -receptor to react, 

 the former with an unsatisfied bond. Since however partheno- 

 genesis can be induced without the addition of fertilizin to the 

 eggs there is no reason for supposing that the egg-receptors 

 united with the fertilizin which was added in my experiments 

 for the purposes of initiation. This however does not seem to 

 me to be at all necessary, for both substances are present in the 

 egg from the beginning and we may postulate a union between 

 the receptors and the fertilizin within the egg. 



If this is indeed the mechanism of both parthenogenesis and 

 auto-parthenogenesis, we must answer the question why the 

 egg was not fertilized before, or what amounts to the same thing, 

 why fertilization occurs at all. 



In speaking of parthenogenetic agents, Lillie (loc. cit.} tells us, 

 they "need only remove obstacles to the union of the amboceptor 

 and the egg-receptor" (p. 527); and in connection with auto- 

 parthenogenesis, that this might result "if the concentration of 

 fertilizin were raised to a certain point, though it is conceivable 

 that no increase in concentration would break down the resistance 

 that normally exists to the union of the amboceptors and egg- 



