24 C. M. CHILD. 



In a few cases it has also been observed that the last eggs of the 

 breeding season show some indications of parthenogenetic de- 

 velopment. These are doubtless eggs which have remained for 

 a relatively long time in the ducts of the parent organism. Under 

 these conditions the egg is cut off from its supply of nutrition, 

 but is still under conditions more favorable to continued existence 

 than those of the external world. As long as the egg continues 

 to live a minimal amount of metabolism is undoubtedly going on. 

 In the absence of external nutrition this metabolism itself must 

 bring about a slight degree of dedifferentiation and when these 

 eggs finally emerge from the ducts they are probably slightly 

 younger than those extruded earlier and therefore react some- 

 what more strongly to the changed conditions by showing some 

 indications of parthenogenetic development. 



The work of recent years on artificial parthenogenesis has 

 demonstrated that other means of stimulation of the egg to 

 development may be substituted for the spermatozoon and it is, 

 I think, sufficiently demonstrated that the essential feature of 

 these artificial methods of stimulation lies in the fact that they 

 make possible a continuation and increase in the metabolism of 

 the egg. Whether they accomplish the result through super- 

 ficial cytolysis or through an increase in the permeability of the 

 membrane is not of prime importance for the present purpose: 

 it is quite possible that some act in one way, some in the other. 

 Certainly it does appear to be true that many of the partheno- 

 genetic agents do increase the permeability of the membranes 

 and if R. S. Lillie's view (Lillie, 'oga, '096, 'n) that the stimula- 

 tion of a cell consists essentially in increase of permeability to 

 COo is correct, it is not improbable that the effect of at least 

 many of the parthenogenetic agents on the egg is of this nature 

 and therefore not in any sense specific. According to the view 

 of reproduction developed in this paper, there is absolutely no 

 reason to suppose that it is specific. Moreover, I cannot agree 

 with Loeb ('09) that it is any more a formative stimulus than any 

 other. It is primarily a stimulus to metabolism and the formative 

 changes are an incident or result of continued metabolism. 



But in any case the methods and agents of artificial partheno- 

 genesis merely serve to initiate the processes of dedifferentiation 



