PAR THENOGENESIS 



that of experimentally induced and naturally occurring 

 parthenogenesis as well as that of fertilization, the estab- 

 lishment of the first mitotic figure is brought about by a 

 dehydration of some constituent of the ground-substance, 

 or as the result of a reaction between nuclear and cytoplas- 

 mic ground-substance brought about by dehydration. The 

 mitotic figure then is either expressly a dehydration-for- 

 mation or the result of a reaction rendered possible by 

 dehydration. In the resting Qgg this material in the 

 ground-substance is spatially diffused; with the process of 

 parthenogenesis or of fertilization it becomes aggregated — 

 in parthenogenesis and in some cases of fertilization around 

 the egg-nucleus, in most cases of fertilization around the 

 sperm-nucleus. What we see as asters and as spindle may 

 be either this material itself or the sign or product of its 

 activity. 



This hypothesis — and more can not be proffered in the 

 present state of our knowledge — is wholly consistent with 

 the established facts as far as one can reduce them to order. 

 According to it the most important factor in all modes of 

 initiating development is a dehydration-process affecting 

 directly or indirectly the ground-substance.^ In all cases 

 of the initiation of normal development, dehydration begins 

 in the ectoplasm. 



Ectoplasmic changes alone, as I have shown above, are 

 not experimental parthenogenesis. They do not of them- 

 selves determine that development will follow; but they are 

 a reliable indicator for the quality of the development, if 

 this ensues. That there are cases of ectoplasmic changes 

 without subsequent development on the one side and that 

 the sea-urchins' egg after treatment with weak hyper- 



^ Delage in igoib promulgated a dehydration-theory of fertilization; 

 but this differs from the one here proffered in ascribing dehydration 

 to the influence of the sperm only. 



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