Hinckley.] . • 94 [October 4, 



frogs have already become wholly lung breathing. The eye is 

 developed ; the pupil has the power of dilatation and contrac- 

 tion. 



June 7. Found many young frogs in the grass along the shore, 

 having the mouth fully developed externally, and the tail reduced 

 to a mere blackened stump. 



June 9. Tail has wholly disappeared, and the tadpoles whose 

 entire length was 58 millim. May 31, having steadily diminished 

 in length and girth since the arms were thrown out, measure 

 to-day as young frogs, only 18 millim. from the muzzle to the end 

 of the body. Obscure spots of dark brown are seen on the throat 

 and breast, which disappear as the young frogs reach maturity. 

 But a small fraction of the gross number of tadpoles hatched, 

 has escaped the numerous enemies and reached the stage of the 

 young frog. 



I have found some difference in the size reached by tadpoles of 

 this species, and the same is true in regard to the rapidity of their 

 development. At a pond distant only about twenty-five rods, 

 tadpoles hatched at the same time began to leave the water a 

 week earlier. 1 The pond is situated in an open pasture, exposed 

 to the sunlight and protected from the north and east winds by 

 rising ground. It is shallow, and evaporates wholly by mid-sum- 

 mer, and at all times responds quickly to the sun's heat, averaging 

 a higher temperature than the deeper and more shaded pond in 

 the woods. But I have observed for many seasons that the tad- 

 poles grown in the deeper body of water average a larger size 

 than those reared in the smaller, shallower pond. The same differ- 

 ence in a more marked degree may be seen between tadpoles of 

 R. catesbeiana taken here in the Neponset River, and those grown 

 in a small pond near it. 



For a short time the little frogs were seen under the growth of 

 herbage about the pond, but soon dispersed to the woods where 

 they were at first numerous, but by the last of August, having 

 distributed themselves more widely, were met with less frequently. 

 Among frogs hatched from the same mass of eggs may be found, 

 as is known, some latitude of variation ; it exists not only in the 



!In 1880 the mean temperature for May was 66.02°, the highest for 20 years here. 

 In the colder seasons of 1881 and 1882 it was 59.01° and 5]. 34° and R. sylvatica was 

 10 and 11 weeks in passing through the larval stages in these localities. 



