SPERMATOZOA 



69 



cell divides and the various kinds of segmentation in a 

 fertilised ovum. In most cases the spermatogonium 



Yic. 33.— Forms of spermatozoa (not drawn to scale). 



I and 2. Immature and mature spermatozoa of snail ; 3- of bird ; 

 4. of man (h., head ; m., middle portion ; /., tail) ; 5- 01 sala- 

 mander, with vibratile fringe (/.) ; 6. of Ascaris, slightly 

 amoeboid with cap (c.) ; 7. of crayfish. 



divides into spermatocytes, which usually divide again mto 

 spermatids or young spermatozoa. 



YiG, 34. — Diagram of maturation and fertilisation. 

 (From Evolution of Sex.) 



A. Primitive sex cell, supposed to be amoeboid. 



B. Unripe ovum ; C. formation of first polar body (i. p.b.) ; D. forma- 



tion of second polar bodv (2. p.b.). 

 B'. Mother sperm cell ; C the same divided (sperm-morula). 

 D'. Ball of immature spermatozoa ; sp., liberated spermatozoa. 

 E. Process of fertilisation ; F. approach of male and female nuclei 



within the ovum. 



Maturation of ovum. — When the egg-cell attains its 

 definite size or limit of growth, it bursts from the ovary or 



