536 



The metamorphosis of the tadpole, when at its full growth, requires 

 about fourteen days to bring it to the condition of a frog. About 

 the termination of that period, the diminution of the body is so great, 

 and also the absorption of the expanded caudal extremity is such, as 

 to diminish cutaneous respiration. Respiration by the lungs becomes 

 absolutely necessary to prevent the animal from becoming asphyx- 

 iated, which would be the case if it remained in the water requiring 

 then not an aquatic, but an atmospheric medium of respiration. It 

 may be observed that after the tail is partially absorbed, leaving only 

 a portion of the solid part, the asphyxiated state has commenced : 

 the little animal, with open mouth, gasps for breath ; but if removed 

 into atmospheric air, the mouth is directly closed, and respiration is 

 effected through the nostrils with perfect freedom ; the animal is re- 

 stored directly, jumps about and is lively. 



3. On the Influence of the absence of Light on the Tadpole and on 

 the Frog. 



This time I commenced my experiments in three rock cellars, 

 formerly only in one. 



The cellars in Nottingham, cut out of solid rock, are most favour- 

 able for experiment; no solar light ever enters, and they are not 

 subject to any great change of temperature. The deepest cellar is 

 30 feet deep, the mean temperature 51 Fahr. ; the middle cellar is 

 18 feet deep, its mean temperature 53 Fahr. ; the uppermost cellar 

 9 feet deep, mean temperature 56 Fahr. 



June llth. In each cellar I placed a shallow glazed earthenware 

 vessel, containing two pints of water, with grass for chlorophyll for 

 food, changing the water every second day. In each vessel I put 

 twenty tadpoles, approaching the period of their metamorphosis, fol- 

 lowing the example of Dr. Edwards, a much easier method than 

 commencing with the spawn. 



In the uppermost cellar ten were fully developed in the form of a frog 

 on the 8th of September, and were on the stones, having left the water. 



In the middle cellar ten were fully developed on the 22nd of 

 September. 



In the lowest cellar eight only had left the water, being fully 

 developed on the 20th of October. 



In the following year, July 1st, I made a similar experiment in 



