STRUCTURE AND FUNCTION IN MAMMALIAN EGGS 



35 



degenerating. There is no evidence that these eggs can undergo any 

 kind of true embryonic development, though concomitant break-up 

 of the cytoplasm may have a superficial likeness to cleavage (p. 84). 



1 >*4 1 ,*<"ii * 



- • # 



S.N. 



S,N 





.'<? 



Fig. 28 

 (<i) Vitelline chromosome group (Chr.) becoming scattered after emission of the second 

 polar body (2.Pb.) in a rat egg. X 1,000. (b) and (c) Subnuclei (S.N.) of various sizes near 

 apparently normal male pronuclei (£). X 800. (From Austin and Braden, 1954b.) 



Since subnuclei are probably derived from scattered chromo- 

 somes, and chromosomes may go astray even under apparently 

 normal circumstances, it is not unexpected that subnuclei are 

 occasionally found in eggs undergoing otherwise normal fertiliza- 

 tion or cleavage. It seems very likely that the chromosomes involved 

 in subnuclei would not enter into syngamy in a normal manner and 

 may even fail to take part at all. If this is so, the resulting embryo 

 could come to carry chromosomal anomalies such as mosaicism or 



