The Cellular Basis 



139 



is possible in a few instances to distinguish the chromosomes of 

 the egg from those of the sperm, and in every instance where this 

 can be done it is perfectly clear that these chromosomes do not 

 fuse together nor lose their identity, but that every chromosome 

 splits lengthwise and its halves separate and go into the two 



H 



FIG. 44. MATURATION AND FERTILIZATION OF THE EGG OF THE MOUSE.' 

 A, First polar body and second maturation spindle. B, second polar body 

 and maturation spindle. C, Entrance of the spermatozoon into the egg. 

 D-G, Successive stages in the approach of egg and sperm nuclei. H, for- 

 mation of chromosomes in each germ nucleus. /, First cleavage spindle 

 showing chromosomes from egg and sperm on opposite sides of spindle. 

 (After Sobotta.) 



