324 



PHYSIOLOGY OF GONADS 



point of reference, the cycle can be divided 

 into 6, 8, 12, or more phases. 



Roosen-Runge (1951-1955), Roosen- 

 Runge and Barlow (1953j, and Roosen- 

 Runge and Giesel (1950) used eight phases 

 to characterize a seminiferous cycle in 

 the rat. In phase 1, no sperm cells are 

 present in the tubule; at the end of phase 

 8, the sperm cells forming over the inter- 

 vening phases have disappeared from the 

 lumen. Two types of spermatogonia are 

 recognized; type A is a large cell with 

 a large nucleus and little chromatin, and 

 type B is a smaller cell with a smaller 

 nucleus and masses of chromatin arranged 

 peripherally. Type A spermatogonia divide 

 simultaneously in phase 1 and again at 

 phases 4, 6, and 7, leading to successive 

 doublings. Type B spermatogonia form 

 from type A in phase 6. In phase 8, a total 

 of 98 per cent of all the spermatogonia are 

 type B, leaving a 2 per cent quota of type A 

 to start the cycle over again. When the sper- 

 matozoa are floated off the tubular wall, 

 type B spermatogonia rapidly change into 

 prespermatocytes. The prespermatocytes 

 grow rapidly and become spermatocytes. 

 Spermatid formation occurs in the first four 

 phases. Spermatozoa are present from the 

 end of phase 5 through phase 8. 



Interestingly, the Sertoli cells show a 

 cyclic variation in volume, being largest at 

 phases 7 and 8 and smallest at phase 1. 

 Retraction and expansion of the Sertoli 

 cells, with cycles of spermatogenic activity, 

 was noted by Rolshoven (1945, 1947, 1951). 

 When the cells retract, part of the cyto- 

 plasm is lost, leaving a pars basalis. In ex- 

 panding, this part of the Sertoli cell forms 

 a fine lattice. The Sertoli cells resorb re- 

 gressive spermatozoa and probably also 

 the residual bodies during the spermatogenic 

 cycle. 



Because PAS-positive material can be 

 traced back to the Golgi apparatus of young 

 spermatids (Leblond, 1950), Leblond and 

 Clermont (1952a, b) have been able to di- 

 vide spermiogenesis in the rat into 19 stages. 

 In the first 8 of these, the germinal epithe- 

 lium has old spermatids, which are released 

 when the new crop reaches stage 8. Hence, 

 the new crop of spermatids is alone until 

 they reach stage 15, when another genera- 

 ation of spermatids appear. Therefore, stage 



1 and stage 15 spermatids appear together, 

 and the succession of cells associated with 

 this appearance marks one cycle. These 

 authors have divided their 19 stages of 

 spermiogenesis into four phases (Fig. 5.8). 



The first phase is the Golgi phase, which 

 includes 3 of the stages. In stage 1, the idio- 

 some is in the Golgi zone and two centrioles 

 are near the chromatoid body. The fine 

 filament from one centriole eventually be- 

 comes the tail of the sperm. In stage 2, one 

 to four granules appear in the idiosome. In 

 stage 3, the fusion of pro-acrosomic gran- 

 ules into one large one is accomplished. 



The second phase is the cap phase, which 

 consists of 4 stages. In stage 4, the acrosome 

 granule flattens on the nucleus. In stage 

 5, a membrane arising from the granule 

 spreads over the nucleus. In stage 6, a cap 

 is formed over the nucleus. The idiosome 

 separates from the acrosome granule, and 

 the two centrioles move closer to the nu- 

 cleus. In stage 7, the cap reaches maximal 

 size. The proximal centriole adheres to the 

 nucleus, and the flagellum remains attached 

 to the distal centriole. The chromatoid body 

 is loose in the cytoplasm. 



The third phase is the acrosome phase, 

 which includes 7 stages. The caudal tube is 

 present, and the head caps are oriented to- 

 ward the tubular wall. In stage 8, the gran- 

 ule and cap move toward the basement 

 membrane, and the cytoplasm shifts to the 

 opposite pole of the nucleus. The chroma- 

 toid body surrounds the flagellum near its 

 insertion to the distal centriole. In stage 



9, the acrosome granule elongates. In stage 



10, the head cap moves toward the caudal 

 end of the nucleus, and the apical end is 

 pointed. In stage 11, the nucleus and head 

 cap elongate. In stage 12, the nucleus is at 

 its maximal size. In stage 13, the nucleus 

 is thinner, and the distal centriole divides 

 into a dot and ring. In stage 14, the head 

 cap is loose over the nucleus, the cytoplasm 

 condenses, and the sj^crmatid begins to look 

 like a mature spermatozoon. 



The fourth phase is the maturation phase, 

 which consists of 5 stages. In stage 15, the 

 head cap has a finlike membrane; the ring 

 centriole separates from the centriole and 

 forms the middle piece. In stage 16, elonga- 

 tion of the finlike membrane occurs. In stage 

 17. the acrosome and head cap move for- 



