The Wood-frog, Rana sylvatica LcConle. 95 



THE HATCHING PERIOD. 



On March 29, 1907, eggs were laid in three ponds; the first, a shallow 

 exposed pond which dried up June 28; the second, deeper, also exposed, 

 which dried up the last of August; the third, a deep, heavily-shaded, 

 permanent pond. A bunch laid in one of these ponds March 29 

 was brought into the laboratory April 1, and in a temperature of 66 to 

 70 degrees hatched within 4^ or 5 days from first deposition. At 

 the same time (March 29) a mated pair laid a bunch of eggs in the labor- 

 atory. The.se hatched under the above temperatures in 4f days. On 

 April 10 the eggs of the three ponds had the tops of the bunches frozen 

 and thus killed. From April 6 to 21 the average maximum air-temper- 

 ature was 39 degrees, the average minimum was 28 degrees, at no time 

 above 46 degrees. On April 22, 24 days after deposition, the eggs in 

 the two exposed ponds were hatched, while those in the shaded pond did 

 not hatch until several days later. 



In 1908 R. sylvatica began laying first in the second and third ponds 

 above mentioned. Often, however, the species la} r s first in the third 

 pond, which is spring-fed, opens earliest, and is least responsive to 

 air-temperatures. In the third pond, the species began laying on the 

 2d of April at a water-temperature of 41 degrees. From April 3 to 5 

 the pond was covered with ice. April 6, ovulation became more brisk. 

 From April 6 to 22 the water averaged 44 degrees. On the 23d the 

 water-temperature jumped to 64 degrees, and by the 25th the eggs were 

 hatching, 23 days after extrusion. In the second pond, egg-laying 

 began April 1, at a water-temperature of 41 degrees. Then came ice, 

 as in the third pond, until April 6, when the bulk of ovulation occurred. 

 Thence onward, to April 23, the water averaged 47 degrees, 3 degrees 

 higher than in the third pond, and the eggs hatched on this date, 22 

 da3^s after deposition. In the first pond the species began April 6 

 under 58 degrees, the water averaged 50 degrees until April 23, the day 

 of hatching, which came 17 days after extrusion. In the laboratory, 

 from April 6 to 8, several pairs laid, and these under temperatures from 

 65 to 72 degrees hatched in 6 or 7 days. 



In 1909, in the second pond, the eggs hatched in 23 days. In 1910, 

 in the third (spring-fed) pond the eggs hatched in 17 days under water- 

 surface temperatures from 50 to 67 degrees, the average was 58 degrees ; 

 temperature of water-bottoms 46 to 61 degrees, average 53 degrees. 

 In the first pond they hatched in 14 or 15 days, the maximum air- 

 temperatures ranging from 43 to 81 degrees, average 61 degrees. The 

 water-surface records were 52 to 73 degrees, average 63 degrees; the 

 water-bottom temperature was 49 to 63 degrees, average 54 degrees. 

 In the second pond one bunch, laid March 27, hatched April 3, only 7 

 days after deposition. The weather was very uniform and the temper- 

 atures were: maximum air-temperatures 62 to 80 degrees, average 70 

 degrees; surface-temperatures 56 to 68 degrees, average 61 degrees; 

 water-bottoms 56 to 64 degrees, average 59 degrees. The bulk of the 



