The Wood-frog, Rana sylvatica LeConte. 



91 



For the day previous to the record, we find no maximum air-tempera- 

 tures below 43 degrees and an average of 53 degrees; for the day of the 

 record, a low temperature of 41 degrees and an average of 58 degrees. 

 Each record is flanked on one side by 45 or more. It appears that 

 when the air-temperatures begin to approach 43 to 45 degrees, we may 

 expect the frogs to lay eggs. An average date of spawning would be 

 about April 4; our earliest record is March 19, 1903; our latest first 

 record, April 14, 1900. In general, wood-frogs spawn most in the first 

 half of April, though occasionally earlier or later in some years. 



In some earty springs, usually the last of March, the spawning- 

 begins with a rush and the species may be practically through laying 

 within 4 to 6 days after the beginning of ovulation. In 1907 and 1910, 

 we had good illustrations of this condition in the eight or nine localities 

 under observation. A summary of the egg-complements for these 

 years follows: 



Iii these instances, as in many others of early spawning, the bulk of 

 egg-laying may be completed by April 1 and then 3 to 4 weeks may inter- 

 vene before a straggling record appears the latter part of April. Our 

 latest records for spawning are: April 27, 1906, when no eggs were laid 

 for two weeks previous; April 25, 1907, 23 days interval; April 24, 1908, 

 no interval; April 30, 1910, 29 days; April 20, 1911, no interval. It 

 will be observed that in 1908 and 1911 no intervals are recorded; in 

 each of these the spawning began later in April. In 1908 it began 

 April 1 and continued to April 24; in 1911 it started April 6 and ran 

 continuously to April 20. In each, inasmuch as the spawning begins 

 later, it bridges the mid-April gap, which appears in the earlier spawn- 

 ing seasons of this species. Furthermore, when the species begins late 

 the continuous spawning record is stretched over two or three weeks 

 instead of one, as in the earlier seasons. 



In 1908, we began taking water- temperatures to determine the effec- 

 tive warmth necessary to start and to bring to a crest the spawning. 

 In four different ponds, the species gingerly began at 41 degrees. When 

 the water ascended to 48 degrees several records came, but it reached 

 the crest in three different localities at temperatures of 53, 54, and 58 



