MAMMALIAN TESTIS 



317 



cells. Abnormal forms of sperm cells appear 

 in the semen, reflecting the degeneration of 

 the germinal epithelium at this time. The 

 volume of the semen decreases, and libido 

 is depressed. Thus, the ram may be regarded 

 as an annual breeder, but the regression in 

 the nonbreeding season is not complete 

 (Maqsood, 1951a). Even the laboratory 

 rat shows some evidence of a seasonal 

 rhythm (Gunn and Gould, 1958). The ca- 

 pacity of the dorsolateral prostate to con- 

 centrate injected Zn*^^ is greater in Febru- 

 ary-March and June-July than at other 

 seasons of the year. 



Various species of squirrels have been 

 favorite subjects for the investigation of 

 certain features of seasonal breeders (Moss- 

 man, Hoffman and Kirkpatrick, 1955; 

 Kirkpatrick, 1955.1. The testes of the in- 

 fantile fox squirrel contain small, round, 

 lumenless cords with a single row of sper- 

 matogonia, Sertoli cells, and a few sper- 

 matocytes. The Leydig cells are undiffer- 

 entiated. The prepubertal fox squirrel has 

 larger tubules with lumina. The testes at 

 this time have increased about five times 

 in weight, and the tubules are twice their 

 former diameter. Spermatids are present. 



The mature fox squirrel has free sperm cells 

 in rather wide lumina, and mature, large 

 Leydig cells. In the nonbreeding season, the 

 spermatids and spermatozoa degenerate, 

 leaving only spermatogonia, Sertoli cells, 

 and a few spermatocytes. The tubular wall 

 becomes contracted and thickens, causing 

 the shape of the tubule to be irregular. The 

 Leydig cells atrophy. In December and Jan- 

 uary, when the breeding season starts, the 

 process of sexual maturation is repeated. 

 This process recurs annually ; however, with 

 each year, the tubular wall becomes more ir- 

 regular in shape demonstrating that periods 

 of maturation and degeneration have taken 

 place previously. 



V. Architecture of the Testis 



The testis of most mammals is divided 

 into lobules by means of septa, and the en- 

 tire testis is enveloped by the tunica al- 

 buginea, which keeps it under pressure. 



The testis of the rat, however, has no 

 septa; instead, the organ is constructed in 

 a fan-shaped manner from a series of 

 spiral canal arches, which arise from the 

 rete testis (Fig. 5.5). The tubule is a U- 

 shaped structure, open at two ends to the 



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i : 



Li>t^-^' ^M?-Vtt^^ 



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Fig. 5.5. Architecture of rat testis, showing relationship of tubules to spermatic artery. 

 and arrangement of the Leydig cell aggregates and capillaries. (From I. MUller, Ztschr, 

 Zellforsch. mikroscop. Anat., 45, 522, 1957.) 



