32 



PRINCIPLES OF EMBRYOLOGY 



in the first place contain sufficient reserves of nutriment to keep the young 

 animal aHve till it can obtain its own food, and although some of these 

 stores can, as we have mentioned, be provided outside the egg-cell proper, 

 yet in most cases such an expedient is only resorted to after the ovum 



Figure 2.2 



Structure of a typical mammalian spermatozoon (that of the ram). On the 

 left a light microscope picture of a complete sperm, on the right an interpre- 

 tation of the structure of the middle piece as revealed in the electron micro- 

 scope. (From Randall and Friedlaender 1950.) 



itself has been loaded to capacity. Further, apart from reserves of food, 

 the egg cytoplasm must embody in some way the structural basis out of 

 which the embryonic body can be formed; and this, one can see, must 

 involve an elaborate process of preparation. It is not surprising, therefore, 



