GAMETOGENESIS AND SPOROGENESIS 215 



undergo two successive divisions: the first division results in two cells 

 called secondary spermatocytes; the second divides the two secondary 

 spermatocytes into four spermatids, each of which then becomes trans- 

 formed into a spermatozoon. The mitoses in the spermatocyte are meiotic 

 in character and bring about a reduction in the chromosome number. 

 Besides the spermatogenous cells, the testis also contains certain accessory 

 cells, such as the Sertoli cells of mammals and Verson's cells of certain 

 insects. 



The transformation of the spermatid into a spermatozoon (spermio- 

 genesis) has long been one of the most fascinating and difficult problems 

 in structural cytology. The several components of the cell undergo an 

 astonishingly complicated series of transformations, and these, together 

 with the types of spermatozoa resulting, differ considerably in detail from 

 group to group. This has naturally led to much confusion in the literature 

 on the subject, although many points were well covered by the early 

 investigations. The outstanding researches of Bowen (1920-1926) have 

 so clarified our conceptions that his descriptions will be used as the princi- 

 pal basis of the following account. Bowen worked chiefly with insects 

 (Hemiptera, Orthoptera, Lepidoptera, Coleoptera, Aptera) and amphibia 

 (Plethodon), but comparisons show that his descriptions, with minor 

 modifications, will apply to the general features of spermatogenesis in 

 various other groups. -"^ 



The Spermatocyte and Its Divisions (Fig. 129). — In the spermatocyte 

 are the following components: nucleus, cytoplasm, chondriosomes, Golgi 

 material, a pair (usually) of centrioles, and frequently other formed ele- 

 ments of questionable nature. The chondriosomes are present in the 

 form of granules, rods, or threads, and, although these behave variously 

 in different species, they are usually distributed rather equally to the four 

 spermatids in the two divisions. This in some cases involves the passive 

 division of individual chondriosomal threads or an even more precise 

 distribution (p. 86). The centrioles diverge to opposite sides of the cell 

 and occupy the poles of the achromatic figure in each mitosis. At the 

 close of the second mitosis the centriole usually divides, so that the sper- 

 matid has a pair of them. Much confusion in terminology and diversity of 

 interpretation have arisen concerning the special differentiations which 

 may occur about the centrioles and the topographic relation which certain 

 other cell components, notably the Golgi material, may bear to them. 



Two general modes of arrangement of Golgi material in spermatocytes 

 may be distinguished. In the insects (Bowen) a number of Golgi bodies, 



^1 For further general accounts of animal spermatogenesis, see Wilson (1925), 

 Metz (1932), and the resume by Bowen (1924c). See the extensive researches of 

 Gatenby (1917 et seq.). Other recent works are those of Voinov (1925, 1927a6), Nath 

 (1925), Chickering (1927), Sokolow (1926, 1929a6), Payne (1927), Hirschler (1928), 

 Pollister (1930), and H. H. Johnson (1931). 



