COLD-BLOODED VERTEBRATES 



1069 



structures. Such an interpretation would 

 seem applicable as well to the results ob- 

 tained in Sceloporus. 



In the garter snake (Hartley, 1945) sex 

 differentiation, as previously stated, nor- 

 mally occurs between the 16th and 19th day 

 of pregnancy. To study the effect of sex 

 hormones, testosterone propionate or es- 

 tradiol di[)ropionatc was injected during 

 the first month of pregnancy, either into 

 the peritoneal cavity of the mother or into 

 the amniotic sacs. For some reason, intra- 

 peritoneal injections had no effect on the 

 young. Intra-amniotic androgen increased 

 the rate of spermatogonia! mitoses and 

 growth of seminiferous tubules. This hor- 

 mone prevented regression of the ovarian 

 medulla but checked development of the 

 ovarian follicles. Estrogens reduced the 

 size of the seminiferous tubules but caused 

 no change in the ovary. Miillerian duct hy- 

 pertrophy was seen during the last month 

 of gestation in females injected with estro- 

 gen and androgen. Parturition did not occur 

 if estrogen had been injected; the reason for 

 this failure was not clear. 



Sex hormones have also been injected into 

 the immature alligator (Forbes, 1938a, b, 

 1939). Estrone injections for 80 days evoked 

 conspicuous hypertrophy not only of the 

 ovarian cortex but also of the cortical ves- 

 tiges on the testis. The oviducts of the 

 treated females became so huge as to oc- 

 cupy most of the abdominal cavity, and 

 persistent Miillerian duct segments in the 

 injected males also showed much growth. 

 Treatment with testosterone and testoster- 

 one propionate was followed by hypertro- 

 phy of the oviducts, penes, and clitorides. 

 Curiously enough, neither hormone affected 

 the mesonej)hroi or their ducts. 



As Dantchakoff (1938) points out, sex 

 hormones may play an imjiortant role in 

 the differentiation and development of the 

 reproductive system of reptiles, both during 

 and after embryonic life. Whereas experi- 

 mental treatment by no means duplicates 

 the normal release of endogenous sex hor- 

 mones, it is likely that the latter are 

 produced in significant quantity during de- 

 velopment. This hypothesis should be in- 

 vestigated in the reptile, perhaps by tech- 

 niques which have already shown their 



value in comparable studies of other ver- 

 tebrate classes. Discovery of the mecha- 

 nisms of sex reversal and of normal morpho- 

 logic sex differentiation still challenges the 

 l)iologist. 



XXIV. Addenclum 



Fish 



Seasonal development of the gonads of 

 the Japanese cyprinodont Oryzias reaches 

 its peak in June and July, and spawning 

 ensues; by September the gonads are of 

 minimal size, recovering during the winter 

 (Egami, 1956). Spawning occurs in late 

 September to early March in the sea gar- 

 fish, Reporhampus, of southern Australia; 

 neither sex usually attains maturity until 

 the age of three years (Ling, 1958). The 

 sea horse, Hippocampus, breeds off the 

 Florida coast from February to October on 

 days having more than eleven hours of sun- 

 shine (Strawn, 1958). The Black Sea mer- 

 ling, Odontogadus, spawns the year around 

 (Burdak, 1955). In the whiting (Gadus 

 merlangus L. ) and Norway pout {G. es- 

 markii Nilsson ) , seasonal development of 

 the gonads occurs from January to May, 

 and spawning takes place in May and June. 

 Cells resembling interstitial cells can be 

 seen in the spent testis, and a corpus lu- 

 teum-like structure has been detected in the 

 ovary (Gokhale, 1957). The selachian cor- 

 pus luteum appears to be functional ( Chieffi 

 and Rattazzi, 1957). 



Administration of methyl testosterone to 

 juvenile male Lebistes provokes early ma- 

 turation of the testis, promptly followed by 

 its degeneration. In adults this compound 

 causes hypertrophy of the sperm duct, in- 

 hibition of ovogenesis, and enlargement of 

 the lumen of the ovarian excurrent duct 

 (Geske, 1956). Testosterone treatment pro- 

 motes growth of the vas deferens and of the 

 dorsal fin rays of both sexes of the file fish, 

 Monocanthus (Ishii and Egami, 1957). Im- 

 plantation of testosterone propionate pellets 

 into females, or of estrone pellets into 

 males, of Oryzias promotes growth of male 

 or female type, respectively, in the inter- 

 neural and interhemal spines and the basip- 

 terygium (Egami and Ishii, 1956). 



Unhatched eggs of Fundulus confliientus, 



