REPRODUCTION 



121 



Primary 



sptrmotocyle r /. 



dividing / . ' 



Spermotogonia 



Primory tpirmotocylt 



% 



Figure 6.4. Diagram of part of a section of a human seminiferous tubule to show 

 the stages in spermatogenesis and in the transformation of a spermatid into a mature 

 sperm. (Villee: Biology.) 



ASCARIS 



Figure 6.5. Eggs and sperm from a variety of animals, illustrating the differences in 

 size and shape. (Partly after Retzius, from Hunter and Hunter: College Zoology.) 



