IX 



The Annual Ovarian Cycle of Acris Crepitans Baird 



HELEN TALLEY FISHER AND A. RICHARDS 



STUDIES on the sex cycles of vvarni-hlooded animals are numerous, but 

 few investigations of similar character have been reported for the cold- 

 blooded vertebrates. Investigators in this general field have followed 

 several lines of research, including the determination of the processes of 

 spermatogenesis and oogenesis, morphological studies of the genital organs, 

 determination of breeding periods and periods of hibernation, the effect of 

 environmental factors on sex cycles, and more recently the relation of the 

 endocrines to germ cell cycles. Studies made of the sex cycles of amphibians 

 are very limited and no work has been published on the species Acns crepi- 

 tans, although an unpublished investigation was carried on in this laboratory 

 by Whaley on the male of the species. The investigations recorded here were 

 concerned principally with the annual morphological changes in the ovaries 

 of mature specimens of Acris, and minor emphasis only is placed upon other 

 phases of the reproductive process. 



In 1905 and 1908 King reported observations on the oogenesis and mor- 

 phology of the ovaries of Bufo lentiginosus, following an earlier work ( 1902) 

 on the follicle sacs of the ovaries of several amphibians, Rana palustris, Hyla, 

 and particularly Bujo lentiginosus. Her account of the morphological features 

 of the ovaries of these forms in the period preceding the maturation of the 

 oocytes agrees in all essential respects with the observations here described 

 for specimens of A. crepitans. Smith (1912) reported a similar study of fe- 

 males of Cryptobranchiis alleghcniensis. He found that eggs about to be- 

 come mature are readily distinguishable by their much greater size and yolk 

 content, a criterion which may be applied to the oocytes of specimens of A. 

 crepitans also. There is a siniilarity in morphological features and cyclic ac- 

 tivity of the ovaries of specimens of Cryptobranchiis alleghcniensis, as Smith 

 described them, with those of specimens of A. crepitans. Alexander in 1933 

 reported on the seasonal variation in the general morphology of the gonads 

 of a tropical toad, Bujo melanostictus. He found, in mature females exam- 

 ined, ovaries in all conditions of growth and maturity at all times of the 

 year, with the exception of October and November. He regarded reduced 

 ovaries in mature females as an indication that the spawning period had 

 occurred a relatively short time previously, and thought the breeding season 

 of the form might thus be determined. More general descriptions of amphi- 

 bian ovarian changes and the morphological features accompanying them are 

 found in the accounts of Morgan (1897), McEwen (1928), Korschelt and 

 Heider (1902), Noble (1931), and others. Kingery (1917) worked on oogene- 



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