1868.] 191 [.yien. 



after severe frosts, and when a subsequent sudden change in the 

 weather must have prevented their reaching the marshes that season. 



The present year (1868), I first heard them (at Cambridge) April 

 1st, and in great numbers, the day being excessively warm. The 

 ground was still frozen in the Museum marsh, while here and there 

 were small banks of snow. At 5 P. M., I found the temperature of 

 the running water in the Museum ditch, 48°, and of still water in 

 pools containing very active individuals of this sj>ecies and of Rana 

 sylvafica, 58°. I give an abstract of some observations which were 

 continued for about two weeks, with a view of determining the lowest 

 temperature at which this and other species of oui* fiogs are active, 

 and begin to spawn. The weather, very warm and very cold days 

 alternating, proved extremely favorable to my piu-pose. 



" April '2d. Last night was very warm, as is to-day, the maximum 

 temperature of 76° being reached at 3^ P. M. Hyla Pickeringu 

 and R. sylvatlca out in great numbers. Chri/seim/s picta and Nanemy» 

 guttata sunning themselves on the banks of the ditches. The marshes 

 not yet fully thawed. 



" April 3d. A smart frost in the morning, and a thin sheet of ice 

 over very exposed water. At 6| A. M. the temperature of running 

 water in the Museum ditch was 34° ; exposed pools of still water 34°- 

 36°; sheltered still water, 40°-41°. No frogs heard or seen. In 

 about two hours II. Pickermcjli began to pipe, and half an hour later 

 R. sylvatica was heard, the warmest water having increased in tem^ 

 perature to above 50°. 



" x\pril 4th. Hard frost in the morning, the ground considerably 

 frozen, and thin ice on very much exposed pools. At 7 A. M. tem- 

 perature of the water beneath the ice, 34°; of running water, 38°; 

 of unfrozen (sheltered) pools, 38° at the surface, and 40° ten inches 

 below the surface. No frogs seen or heard. At 9-^ A. M. running 

 Avater 48°; still water 46°-48°; no frogs. At 11| A. M. running 

 water 50°; still water 52° (48°-54°; where shaded 48°; where it 

 received reflected heat 54°). H. Picleringii and R. sylvatica out sp;u'- 

 ingly; more numerous later in the day. Day rather cloudy, and 

 somewhat raw. Thousands of H. Pickeringu piping during the eve- 

 ning, the temperature of the water being between 50° and 60°. 



•'Saw eggs of ii. sylvatica laid yesterday; a large oblong mass,, 

 eight inches long and four or five wide, attached to the stem of a 

 reclining weed. 



" April 5th. An inch of snow fell just before daylight. Squally at 



