64 



The Pickerel-frog, Rana palustris LeConte. 



THE OVULATION. 



In all the situations where eggs were recorded, clear water obtained. 

 The best places for the observation of spawning were a pond heavily 

 laden with dead leaves and a quiet back-water of one of our streams. 

 In both instances they were connected with a stream in the spring, and 

 then had their own currents; the first became absolutely cut off and 

 quite remote from the stream, while the other ceased as a meandering 

 subsidiary and merely kept its connection with the main channel. 

 We have frequently found their eggs in the shallows of mill-ponds, and 

 occasionally along the rocky shores of lakes. They also have laid in 

 the deep holes of our ravines, particularly below waterfalls, also in 

 lowland pools of the wide valleys of wandering streams. More rarely, 

 did they breed in marshy stretches or in upland ponds disassociated 

 with some creek or watercourse. 



Ovulation usually begins the last week in April. The beginning of 

 spawning for several years is as follows : 



Thus, we see that the maximum air-temperatures range from 51 to 81 

 degrees, and that they average 68 degrees for the day before the record ; 

 for the day of the record, they range from 50 to 82 degrees and average 

 69 degrees. Every record is flanked on both sides by a temperature of 

 50 degrees or more, usually above 61 degrees. A consideration of 

 21 different breeding records (not first ovulations) gives an average of 

 67 degrees for the day of the record and only one record below 53 

 degrees; for the day before the record the average is 65 degrees, with 

 only one individual case below 50 degrees. Every one of these records 

 is flanked on one or both sides by at least 50 degrees. Water-tempera- 

 tures taken at the time and place of breeding yield averages from 57 

 to 60 degrees; the maxima average 64 degrees, the minima 51 degrees. 

 These temperatures, 51 to 64 degrees, well represent the prevailing 

 warmth of the water at breeding. 



The average date of ovulation is April 23; no record precedes this 

 date except one, April 6, 1910. The bulk of the ovulation takes place 

 the last week of April and the first week of May. The species seldom 

 lays beyond May 15. The latest date for eggs was May 16 in 1906; 

 May 18 in 1907; May 12 in 1909. The extreme period of breeding is 



