138 \V. C. CURTIS. 



the " developmental stimulus " to have the resulting oosperm go 

 into a resting state which would result eventually in its death unless 

 the " stimulus to development " intervened to start a new cycle. 

 If this developmental stimulus, or some substitute for it, and its 

 action were accurately known we might apply it at will at any 

 time after the union of the germ-plasms was completed, and so 

 long as the oosperm remained alive it would respond by begin- 

 ning the new cycle of development. 



In the thorough understanding of the two apparently distinct 

 processes involved in fertilization as hitherto understood we 

 should I think be greatly aided by the investigation of the prob- 

 lem just outlined which is the converse of that brought out by the 

 work on " artificial parthenogenesis." 



We have, it seems to me, cases of normal development which 

 are parallel to this converse proposition in just the same way that 

 normal parthenogenesis is a parallel to the artificial development 

 induced by salt solutions and other stimuli. These cases are 

 seen in the development of those forms in which the fertilized 

 egg has a long resting stage. Where freezing or desiccation is 

 necessary for such subsequent development, this condition may 

 be regarded as one of the developmental stimuli, although if one 

 tries to picture how a state of affairs necessitating this particular 

 condition could have arisen in the past he must, I think, feel cer- 

 tain that though extreme cold or dryness may now be a neces- 

 sary factor it must originally have been unnecessary if not a thing 

 fatal to the further existence of the organism. 



Any one familiar with biological literature can readily recall 

 numerous cases of eggs with longer or shorter resting periods 

 following upon the union of the germ plasms. The particular 

 case I call attention to is that presented by those Cestoda which 

 in their development have resting fertilized eggs gradually accu- 

 mulating in the uterus as in the case in BotJiriocepJmlus /afns, Tri- 

 anopJionis nodulosus, Ligulasimplissima, etc., and in Crossobothrium 

 Inclination. On referring to the description which has been given 

 of the production of the eggs and their extra-uterine development 

 it will be seen that this illustrates particularly well what I have 

 termed the converse of artificial parthenogenesis and that the 

 hypothetical case which I set forth on page 137 might be substi- 



