COMPARISON OF OVARIES 



September — The single large specimen available had few growing young 

 oocytes and many large degenerating ones (0.9 diameter, the rule). The ovary 

 was very small in relation to the size of the toad, suggesting the end of the 

 summer breeding period. 



October — All specimens indicated that the summer reproductive period 

 was past. Young developing oocytes abundant, all larger ones degenerating. 

 The drop in ovarian percentages from 20.34 in August to 2.95 in October 

 substantiates the microscopic findings. 



Discussion 



In Bnjo cognatHS in Oklahoma, breeding behavior is initiated by rain- 

 fall at any time between March and September ( Bragg, 1940). In B. w. tvood- 

 hoHsi'i, rainfall stimulates this behavior during this same period, but some 

 females produce eggs each spring (usually during March or April) whether 

 rain falls or not; whereas others do not respond to the spring rains but await 

 the summer months (Bragg, 1940a). The difference in the time of actual 

 production of eggs would seem to lie principally in a difference in the females, 

 since some males of each species usually call after rains; and we might expect 

 these differences also to occur in ovarian volumes and in cytological details. 



Within any month there seem to be variations in the ovarian volume 

 percentage of B. cognatus and B. w. woodhousii (last columns of Tables I 

 and II). These variations are distinctly greater in B. tv. woodhousii than in 

 B. cognatus: and seem to indicate differences in the breeding habits of the two. 



On the basis of the volumetric analysis made here, therefore, Bragg's 

 separation of B. cognatus and B. w. woodhousii into different behavior groups 

 is substantiated. 



The fluctuation in the mean ovarian volume percentage of the mean for 

 body volumes in B. cognatus is not very great from month to month. (Col- 

 umn 5 of Table I, except for April and July.) Since the usual breeding period 

 of B. cognatus (Bragg, 1941a), is from March to September, the volumetric 

 analysis could indicate that, in general, the ovaries would be equally ready 

 for ovulation during these periods. This seems to be the case with the maxi- 

 mum of preparedness for ovulation in April. Though the sudden drop in 

 July of 10.25 per cent is out of line, the discrepancy can be explained. If the 

 collections of July had included animals taken from other sites, the percent- 

 age would very likely have been higher and the range greater. Though repro- 

 duction continues into September, it is to be expected that the tapering off 

 of egg production will be followed by reduced volume. The mean ovarian 

 volume percentage of 22.94 does not bear this out, however; only the micro- 

 scopic evidence is useful in determining that the end of the cycle was 

 approaching. 



The figures in Table II for the mean percentage of ovarian volume to 

 body volumes show noticeable fluctuations from month to month for B. w. 

 tvoodhousii. These evidences are interpreted as indicating that, while there 

 is a general gonadal preparedness for ovulation, individual variation in the 



149 



