THE ACTIVATION OF UNFERTILIZED EGGS 111 



cleavages occur later than normal cleavages (although the 

 time taken for the segmentation process itself is the same in 

 fertilized and unfertilized eggs) . It thus appears that the re- 

 tarded cleavages observed in vivo as the result of semination 

 with irradiated sperm are parthenogenetic in the sense that 

 the sperm chromatin did not participate in the mitoses. 



Novak and Eisinger (1923) attempted to activate rabbit 

 eggs by tying off the tubes at the isthmus to prevent entry 

 of the ova into the uterus. The ova that they recovered 

 were either irregularly cleaved or fragmented with perhaps 

 one or two normal cleavages. Their data thus resemble those 

 of Mann (1924) on rat ova (see Table VIII) which do not 

 descend into the uterus in unmated animals. Grusdew 

 (1896) who injected sperm into the tops of rabbit tubes 

 together with ova from punctured follicles also tied the tubes 

 off at the isthmus and in a number of ova which gave no 

 evidence of sperm penetration he observed ordinarily ir- 

 regular but occasionally regular development. It would 

 seem then that parthenogenetic development may be in- 

 duced in vivo but that extensive embryonic differentiation 

 has not been demonstrated. 



It is obvious, of course, that a mere beginning has been 

 made in the investigation of the parthenogenetic potencies of 

 tubal ova. Presumably normal embryos might develop if a 

 diploid cleavage nucleus could be induced to form. Pincus 

 and Enzmann (1935) have, in fact, found indications that 

 such a process may occur in activated rabbit eggs noting, 

 again, after a rather long latent period, two fusion nuclei in 

 unfertilized ova. The writer has observed an initial nuclear 

 division without cytoplasmic cleavage in a primate ovarian 

 o\nim cultured t/i vitro. For full development in vivo it 

 seems necessary that parthenogenetic ova should duplicate 

 with some exactitude not only the normal morphological 

 changes but also the rate of these processes. For the dif- 

 ferentiating embryo is dependent upon an uterine environ- 

 ment the optimum development of which involves a fairly 

 definite time schedule. 



