36 PROCEEDINGS OF THE AMERICAN ACADEMY 



tained in a trough holding about a barrel of water were intro- 

 duced into a dark closet in a cellar ; the water was occasionally 

 changed, and they were well supplied with food, consisting of 

 Confervas, leaves, grass, and some animal matter. ' The ther- 

 mometer in the closet ranged from 33° to about 60° F. They 

 measured, at the time of introduction, between three and four 

 inches in length ; as they were probably hatched in the spring, 

 they were therefore about six months old. 



During the month of September, 1S52, (ten months after 

 they were introduced into the cellar,) a few were removed to 

 another trough, which, though under cover, was exposed to 

 the ordinary light, and the temperature of the air ; these tad- 

 poles soon exhibited signs of metamorphosis ; their legs were 

 developed and their tails absorbed. 



The remainder have now been seventeen months in the 

 cellar, and if (as there can be little doubt) they were hatched 

 in the spring of 1851, they are now (April, 1853) at least 

 nearly two years old. In the mean time they have not mate- 

 rially changed in size ; the legs, which were mere rudiments 

 when they were introduced, have not increased ; and as far 

 as appears, the tadpoles have no tendency to metamorphosis. 



Assuming the natural larva period to be one year (and 

 this corresponds with observation), that period has in this ex- 

 periment been extended to nearly double its usual duration. 



It was noticed, that when the thermometer was at its greatest 

 depression, the tadpoles exhibited a much greater degree of 

 activity than fully developed frogs, exposed in the same closet 

 to the same degrees of light and heat. The tadpoles were 

 frequently moving about, when the frogs were wholly torpid. 



Tliree linndi-ecl and seventy-eiglith meeting. 



May 3, 1853. — Monthly Meeting. 



The Vice-President in the chair. 



The Corresponding Secretary read a letter from Lieutenant 

 J. M. Gilliss, of the United States Navy, presenting, from the 



