FERTILIZATION. 



35 



described by Wilson. In cases of this type the tail of the spermatozoon re- 

 mains outside the egg while the head and middle piece, almost immediately 



FIG. 23. Fertilization of the ovum of Thalassema. Griffin. 

 ^ , Male pronucleus, **, female pronucleus. 



after entering, turn completely around so that the head points away from the 

 female pronucleus (Fig. 23, a). An aster with its centrosomes next appears, 

 developing from, or in very close relation to the middle piece. The aster and 



