General Account of the Ithacan Anura. 15 



(3 or more degrees above that of appearance), or at water- temperatures 

 of 66 to 71 degrees (9 or more degrees above that of appearance). On 

 the average, breeding comes at average air-maxima of 80 degrees (12 

 degrees higher than appearance data), or at water- temperatures from 

 70 to 71 degrees (13 degrees higher than that of appearance). The 

 minimum interval between first appearance and ovulation is 31 days; 

 the average is 44 days; the maximum interval is 54 days. Our records 

 show that the average date for first eggs is June 28 (we suspect it may 

 prove earlier with several years more of data) ; the earliest record is 

 June 16, and the last is July 10. 



The interval between the spawning season of the two extremes 

 is so great that transformed examples of the first species {Rana sylvatica) 

 are sometimes noted before the last species {Rana catesbeiana) begins 

 laying. In some years, e. g., 1907, transformed individuals of all the 

 species have been found before Rana clamata finished spawning. In 

 Bufo lentiginosus americanus, it occasionally happens that the progeny 

 of the early-breeding toads may transform before the last stragglers 

 of the species lay. 



With six of the eight species, the spawning period usually covers 

 four or five weeks, although the extreme record may be six weeks. 

 Two species, Rana clamata and Bufo I. americanus, may require two 

 and three months respectively for their breeding periods. 



To summarize: The first frogs which appear breed almost immedi- 

 ately after emergence from hibernation, while those which appear last 

 wait long periods before ovulation. In this series of eight species, the 

 intervals between first appearance and fii'st eggs are in an almost perfect 

 ascending scale; and, in general, the order of first appearance is a fair 

 but not absolute index of the order of egg-la3'ing. 



THE EGGS. 



At the outset it was found that pairs mated in the laboratory seldom 

 proved fruitful. A persistent effort was therefore made to secure 

 field-mated pairs for ovulation in captivity. In this way, a certain 

 check was established upon the determination of the eggs deposited in 

 nature, where they were identified by the elimination method and by 

 actual field observations. In the field, we witnessed the whole or a part 

 of the process of ovulation of seven species and the other one species 

 was recognized by the elimination method. In the laboratory, num- 

 erous pairs of six species laid in isolated jars. 



The measurements used in the key were based on fresh eggs, none 

 of which were bej^ond the fine morula stage. The color characters of 

 the vitellus were taken at the time of ovulation with six species, and not 

 later than six or eight hours after ovulation with the other two species. 

 The results of the egg study appear in the table on the following page. 



