REPRODUCTIVE ENDOCRINOLOGY IN BIRDS 



1093 



sion. After ireciucnt multiplication within 

 such cells they become spermatids, thus 

 yielding many spermatids from what 

 started as one cell. He postulated that this 

 phenomenon may explain the formation of 

 sperm clusters. This explanation, indeed, 

 would seem more plausible than the forma- 

 tion of sperm clusters as the result of a 

 chemotactic effect of the Sertoli cells. 



After the spermatozoa have been formed 

 they seem to "bury" their heads in the 

 Sertoli cells. Injection of gonadotrophins 

 into a sexually mature sparrow causes a re- 

 lease of sperm into the tubular lumen. Sucli 

 a release of sperm coincides with the ap- 

 pearance of voided Sertoli cells. Similar 

 changes can be induced in such testes by 

 immersion in hypotonic solution suggesting 

 that sperm release may be due to diffusion 

 of water into the Sertoli cell (Frantz, 1958). 



The seminiferous tubules may have an 

 endocrine function, at least in some birds. 

 The testes of seasonally producing birds 

 show a marked regression at the end of the 

 breeding season, a regression preceded or 

 accompanied by a marked steatogenesis of 

 the tubules. The lipoid material in the 

 tubules shows a positive Schultz test reac- 

 tion for cholesterol (Marshall, 1955). A 

 similar histologic and histochemical ap- 

 pearance can be created by hypophysec- 

 tomy of pigeons (Coombs and Marshall, 

 1956; Lofts and Marshall, 1959), or by the 

 injection of prolactin in sparrows, chaf- 

 finches {Fringilla coelebs), and greenfinches 

 {Chloris chloris) (Lofts and Marshall, 

 1956). Chromatographic assay of testes ex- 

 tracts of intact, photostimulated pigeons 

 with bunched sperm in the seminiferous tu- 

 bules, revealed no detectable progesterone, 

 whereas the testes of the hypophysecto- 

 mized pigeons with extensive steatogenesis 

 of the tubules contained this hormone. 



A bioassay of the blood for progesterone 

 ( Hooker-Forbes test) gave negative results 

 for intact pigeons but positive results for 5 

 out of 6 hypophysectomized pigeons (Lofts 

 and Marshall, 1959). This evidence strongly 

 indicates an endocrine function for the tes- 

 ticular tubules of the pigeon. In pigeons 

 progesterone plays a regulatory function 

 in the induction of incubation behavior 

 (Lehrman, 1958, and his chapter in this 



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FIG. 18.2. The siMTiiiMlo^cllotir cycle n\ I lie duck 

 according to ClciiiKUit (1958). (N = Scrloli cell; 

 G — spei-matoguniuin ; GM ~ spermatogonium in 

 mitosis; / = primary spermatocyte in interphase; 

 L = spermatocyte in leptotene stage; Z — sper- 

 matocyte in zygotene stage; P = spermatocyte in 

 pachytene stage; Sim = primary spermatocyte in 

 metaphase; SII = secondary spermatocyte; 

 Slim — secondary spermatocyte in metaphase. 

 The numbers indicate the stages of the cycle. 

 (From Y. Clermont, Arch. Anut. microscop. et 

 Morphol. exper., 47, 47-66, 1958.) 



book). Thus the secretion of progesterone 

 by the testicular tubules may have evolved 

 in this group of birds, whereas in species in 

 which the male does not incubate the eggs 

 or in which progesterone does not induce 

 incubation behavior, this adaptation may 

 be absent. One is reminded of this by the 

 fact that, contrary to Lofts and Marshall 



