124 



PHYSIOLOGY 



CHAP. 



and in the successive stages of their evolution transform them- 

 selves into spermatogonia, spermatocytes, and spermatids, the last 

 of which change into spermatozoa. These different phases of 

 metamorphosis of the sexual cells are represented in their various 

 stages in Fig. 20. 



During their transformation into spermatozoa, the spermatids 

 contract special relations with the cells of Sertoli growing to 



FIG. 20. Diagram of a section of a convoluted seminiferous tubule of a mammal to show the 

 evolution of seminal cells. The tubule is supposed to be divided into eight sectors, in each of 

 which are represented successive stages of the development of the spermatozoa (according to 

 E. A. Schafer). a' a", cells of Sertoli ; a, spermatogonia ; b, spermatocytes ; c, spermatids ; J, 

 parts of the body of the spermatids which are dissolved when the spermatozoa are mature ; 

 s, group of spermatozoa with granules in between derived from the destruction of one part of 

 the body of the spermatids. Some sectors, specially 2, 3, 4, 5, give a clear idea of a sper- 

 matoblast, formed from a cell of Sertoli, a', and of a group of spermatids, c, transforming 

 themselves into spermatozoa. In the sectors 6, 7, 8, 1 are seen groups of spermatozoa at a 

 stage of development far more advanced, with the tails directed towards the free part of the 

 tubule, flanked by young spermatids of the subsequent generation. 



their distal parts to constitute the so-called spermatoblast. It is a 

 cellular copulation (analogous to that observed in many invertebrate 

 animals) which influences the nutrition, and the transformation of 

 the spermatids into spermatozoa. When this has occurred, the 

 spermatozoa detach themselves from the spermatoblast and become 

 free in the lumen of the tubule. 



The spermatozoa of man are filaments 50-55 p long, in which 

 may be distinguished a head and a tail formed of different segments 



