STRUCTURE AND FUNCTION IN MAMMALIAN EGGS 65 



resembling elements identified as Golgi material. During fertiliza- 

 tion and cleavage, the distribution became more general. Odor 

 reported that the characteristic Golgi complex was never seen in 

 secondary oocytes and ootids. 



Fig. 53 

 Loss of light refraction at the surface of a penetrated golden-hamster 

 egg (right). X 130. (From Austin, 1956c.) 



Cortical granules. Low-power examination of hamster eggs with 

 dark-ground illumination shows that the vitelline cortex refracts 

 light much more before than after sperm penetration (Fig. 53). The 

 cause evidently resides in the possession by the cortex of numerous 

 small granules, in impenetrated but not in penetrated eggs. The 

 granules were estimated to be mostly between o-i and 0-5 {jl in 

 diameter and to number 50 to 100/ 100 /x 3 of egg surface (Austin, 

 1956c). In their size, number and evident response to sperm penetra- 

 tion, the cortical granules in hamster eggs are similar to those in 

 sea-urchin eggs; when examined by high-power phase-contrast 

 microscopy, the resemblance in appearance between the cortical 

 granules of the two species is quite striking. Hamster cortical 

 granules, however, appear to be uniform in structure, except for 

 small variations in size, whereas the sea-urchin cortical granules 

 seemed, according to Endo (1952), to have light and dark halves. 

 The fine structure as determined by electron microscopy also 

 appears to differ, the hamster cortical granules presenting little 

 internal detail (Fig. 54), in contrast to the strikingly cristiate structure 

 of the sea-urchin cortical granules (see Afzelius, 1956-7). Hamster 

 cortical granules are thought to play a role in the zona reaction 

 (p. 92). 



Division apparatus. The cytoplasmic organelles concerned with 

 the division of the nucleus are the centrosomes, asters and spindle. 

 The centrosome is best known in non-mammalian eggs; it is 



