54 



THE MAMMALIAN EGG 



In some animals, distinct changes in the pattern of cytoplasmic 

 particulates follow sperm penetration ; these have been described in 

 the bat and guinea-pig (Van der Stricht, 1923), the rhesus monkey 



Fig. 38 

 Guinea-pig egg. X 550. 



**&Mm 





* 



Fig. 39 

 Egg of common pipistrelle bat, with late telophase 

 second-meiotic spindle. X 900. 



(Lewis and Hartman, 1933, 1941), the mouse (Gresson, 1941) and 

 the rabbit (Nihoul, 1927; Austin and Bishop, 1957b). 



Yolk material may become extruded from the cytoplasm and 

 accumulate in the perivitellinc space; the process is known as 

 deutoplasmolysis and is thought to represent either a disposal of 

 superfluous yolk that might otherwise interfere with cleavage, an 

 adjustment of the nucleocytoplasmic ratio or the provision of 

 nutrient materials for the developing embryo. The extruded yolk 



