CHAPTER VII 



The Cytoplasmic structures in Spermato genesis 

 and Oogenesis 



i . SPERMATOGENESIS 



Y N the foregoing account of the maturation phenomena of 

 JL spermatozoa and ova attention has been directed almost 

 exclusively to the nuclear changes ; it will now be necessary 

 to turn aside for a space, in order to consider some of the 

 cytoplasmic processes characteristic of the development of 

 the germ-cells, before describing the behaviour of these 

 cells in fertilisation. 



During the two cell-divisions which take place in the 

 development of each primary spermatocyte into four sper- 

 matids, important changes commonly occur in the cyto- 

 plasm in preparation for the peculiar structure of the mature 

 spermatozoon. The nature of these changes will perhaps be 

 best understood if a short description is first given of a 

 typical spermatozoon. With a few conspicuous exceptions, 

 for example in the Nematode worms and the higher Crus- 

 tacea, the spermatozoa throughout the animal kingdom 

 are built on a common plan, although there are of course 

 great differences in detail between those of members of 

 different groups, or even of different species within one 

 group. A typical spermatozoon consists of three parts, 

 usually called head, middle-piece and tail. The head varies 

 greatly in shape in different animals; it is perhaps most 

 commonly oval in outline, but may have the form of an 

 elongated rod, straight or sometimes bent, or it may be 

 twisted into a cork-screw shape or have other peculiar 



