The Wood-frog, Rana sylvatica LeConte. 89 



THE MATING. 



At the approach of the breeding season, the males have the thumb 

 much swollen and the webbing in the hind feet with margin convex, not 

 concave as in the females at all seasons and in males at other seasons 

 of the year. In fact, this web character is sufficient to distinguish 

 the males at a glance. The males are also usually with a darker colora- 

 tion than the quiet, less active females. At times, even in the daylight, 

 the females may be as light as any Hyla pickeringii of the night. 



The period of mating has begun in some years as early as the middle 

 of March and may rarely extend to May 1. The species is customarily 

 at the height of sexual ardor the last week of March or the first week 

 in April. They mate by day or more frequently during the night. 

 Some of the most vigorous of matings have taken place at noonday with 

 full sunshine, in early morning, midforenoon, or midafternoon. 



The customary Rana embrace (Plate n, Fig. 2) has been recorded in 

 every pair observed. The early eggs laid soon after ice has left the ponds, 

 the apparent coincidence of appearance from hibernation and first egg- 

 records, and actual records of the beginning of embrace and ovulation 

 substantiate the conclusion that this species does not usually remain in 

 the embrace several days before spawning. In the case of most of the 

 mated pairs captured in the field, the egg-laying came the evening 

 following the capture; in one case of a pair mated in the laboratory, 

 ovulation came 1| hours after the beginning of embrace; in four field- 

 mated pairs, they laid not on the evening of capture, but in the fore- 

 noon of the following day; in one case, a pair waited until the second 

 evening after the capture; another pair, 48 hours; and finally, the long- 

 est period recorded was of a pair which waited 4 days. 



Wood-frog pairs separate after ovulation, as is common with all 

 Anura. Occasionally it happens that a male which has once mated 

 will resume an embrace with a spent female, a condition suggesting the 

 possibility of such males mating in nature the second time. In labora- 

 tory, 3 such instances have been observed, one pair continuing for three 

 days in the second embrace. Such embrace, however, because of the 

 weakened condition of the male, may not at first be normal. Once a 

 male grasped a female wrong end to, the forearms being about the loins. 

 Later it resumed the customary embrace. Rarely these males will 

 croak beneath the water from two to six times at a period. Sometimes 

 a fresh male will embrace a spent female apparently without discerning 

 the condition of its mate. 



The tenacity of the embrace may be very pronounced. Mated pairs 

 captured afield have seldom broken, however handled. They have 

 withstood journeys of 2 or 3 miles without separation. They can be 

 fixed in copula by the slow addition of chloral hydrate. Once, in its 

 absence, with NaCl and chloroform such a preparation was made, 

 though the male relaxed slightly. Because of the short period of 



