8 INTRODUCTION TO SEXUAL PHYSIOLOGY 



or about yj,- of an inch), while there are all gradations up 

 to the egg of the ostrich which is more than 3 inches in length, 

 and that of the Japanese shark which is over 8 inches. In 



Fig. 4.— Human ovum, x about 500. (From Waldeyer.) It shows yolk 

 granules in the centre surrounding the nucleus (which, like other 

 cells, contains a more deeply staining spot or nucleolus) and a clearer 

 peripheral portion. It is enclosed by follicular epithelial cells. 



all species, however, the ovum, like the spermatozoon, consists 



of a single cell with nucleus and external protoplasm or cytoplasm. 



Both the ovum and the spermatozoon, prior to uniting together 



in the act of fertilisation, undergo a process of maturation. This 



