116 MAMMALIAN FERTILIZATION 



(Courrier, 1923; Bacsich and Wyburn, 1945) and in the ovary 

 of human to the four-cell stage (Krafka, 1939) has been reported. 

 It is probably induced by some abnormal growth or degenerative 

 changes as shown by the thickening of the granulosa layer of the 

 follicles ( Plate 1,3). The cleavage of unfertilized tubal eggs has 

 been reported in the mouse (Charlton, 1917), the rat (Mann, 

 1924; Austin, 1949), and the ferret (Chang, 1950a). In the rabbit 

 egg, it has been observed on rare occasions a long time after ovu- 

 lation (Chang, 1950a). It may be a manifestation of abnormal 

 cytoplasmic or nuclear activity under certain conditions before 

 degeneration. An ovarian rabbit egg cultivated in vitro by 

 Champy ( 1923 ) cleaved into 8 regular blastomeres in the absence 

 of sperm or any other obvious stimulation. Pincus ( 1930 ) re- 

 ported 63% of unfertilized rabbit eggs divided in a regular way 

 and were indistinguishable from the behavior of fertilized eggs. 



As in the case of artificial activation of eggs in the lower organ- 

 isms, hyper- or hypotonic solutions, butyric acid, or heat were 

 successfully employed to activate rabbit eggs (Pincus and Enz- 

 mann, 1936; Pincus, 1939). Although anesthesia of the females 

 can also induce the activation of rat eggs, probably owing to the 

 lowering of body temperature ( Thibault, 1949 ) or to the produc- 

 tion of cellular anoxia ( Austin and Braden, 1954b ) , it was found 

 that application of cold either in vivo or in vitro is most effective 

 (Pincus and Shapiro, 1940; Thibault, 1949; Austin and Braden, 

 1954b; Chang, 1954). 



The cleavage of eggs to a few blastomeres is quite common 

 after artificial activation. Cleavage up to morula and blastocyst 

 is rare. One 12-celled egg and two blastocysts were obtained by 

 Pincus (1939) when unfertilized eggs were treated with hyper- 

 tonic solution and then transferred into the Fallopian tubes. One 

 collapsed blastocyst was photographed (Pincus and Shapiro, 

 1940), and one morula and three blastocysts (Thibault, 1949) 

 were found in the rabbit when the Fallopian tubes were previ- 

 ously cooled. However, Chang (1954) has shown that by storage 

 of unfertilized rabbit eggs at 10° C. for one day, 18.6% of 145 

 eggs developed into blastocysts when transferred into the Fal- 



