80 



The Bullfrog, Rana catesbeiana Shaw. 



at this date was not at the height of the sexual impulse, even though 

 mated in the laboratory with water-temperatures higher than in the 

 ponds -all of which is confirmed by the first record of eggs laid in 

 the field in 1906. These were deposited at least a week and a half 

 later. The males begin croaking 15 or 30 days before actual spawning 

 takes place. In 1906 an interval of 19 days came before spawning; 

 in 1907 it was 21 days; and in 1908 it was 30 days. About small lakes, 

 mill-ponds, or in swampy creeks, the males may take special croaking 

 stands almost invariably near where there is brush in the water or 

 limbs extending into it. I have known males to keep about one particu- 

 lar spot for 20 days in succession. Whether this same habit obtains 

 for those inhabitants in our deeper swamps remains to be ascertained. 

 Certainly when the species is numerous it may be otherwise. On the 

 16th of June, 1913, when the bullfrogs were laying freely in one lake, 

 we found as many as 10 males within a space of 8 feet. Here among 

 the dead branches of overhanging elderberry bushes they were hidden 

 because of the dense mat the shrubs made. At this time in mid-day we 

 had no difficulty in capturing, by hand, in half an hour, some 25 males, 

 while of females we saw only 3 or 4. Later in the season the females 

 appear more in evidence. Doubtless these easy captures were naturally 

 due to the fact that it was their breeding season. I am, however, 

 coming to believe that this species is as easy of capture as any other 

 Rana. Even after a bullfrog has left the water's surface, one may 

 capture it while it is swimming beneath the water, for they are very 

 slow as compared with some of the other forms. 



THE OVULATION. 



This species lays the last of June or in July. The egg-records for the 

 past few years are shown in the accompanying table. 



The maximum air-temperatures 

 prevailing the day before the record 

 range from 71 to 89 degrees, and 

 average 8 1 degrees ; for the day of the 

 record, they vary from 72 to 92 de- 

 grees or average 83 degrees. Each 

 record is flanked on both sides by 

 maxima of 71 degrees or higher. 

 The water-bottom temperatures for 

 these dates range from 66 to 74 

 degrees or average 70 degrees; for the day previous they range from 67 

 to 74 degrees or average 71 degrees. If, then, we assert that a water- 

 temperature of 66 to 70 degrees must obtain for first ovulation and that 

 more often 70 to 74 degrees proves the prevailing temperature, it is a 

 conservative determination, for this species lays on the surface of the 

 water where the temperature might be higher than the above tempera- 

 tures of the water's bottom. 



