432 MR. HIGGINBOTTOAI ON THE INFLUENCE OF PHYSICAL AGENTS 
in an earthen vessel enveloped in four or five folds of black calico, so as to exclude 
the light, the mean temperature of the room being 6o° Fahr. I placed the same 
number under a shed where the mean temperature of the atmosphere was 60°, and a 
similar number in the deep, dark rock-cellar then at a constant temperature of 55°. 
In six days several of the tadpoles in the vessel in the room at 65° and in the open 
air at 60° were dead, and on examination I found that their branchiae were absorbed, 
and their opercula nearly closed, and I concluded that they had died of asphyxia. I 
now took the precaution to place a stone in the centre of each vessel, so as to allow 
the tritons to leave the water as they lost their branchiae. Two days afterwards the 
top of the stones had a number of tritons upon them in the vessels in the room and 
in the open air. 
All those placed in the rock-cellar retained their branchiae, not one having left the 
water, although I had placed stones for that purpose. No more tritons died after the 
stones had been placed in the vessels, as they afforded them the opportunity of leaving 
the water when the branchiae were absorbed. 
In about twenty-one days afterwards, during the month of September, two or three 
had left the water and were on the stones placed in the vessel m the cellar, fully 
proving that the animal came to its full development in the absence of light, though 
this development was retarded by the low temperature of 55°. 
Exp. 4. — On the 25th of August I deprived three tritons, one of an anterior, another 
of a posterior extremity, and the third of the tail. I put these into a vessel, which I 
enveloped in five or six folds of black-glazed calico so as to exclude the light, and 
placed it in a dark part of a room where the maximum temperature was 70° Fahr. 
As it was then the time of the year when the full-grown tritons leave the water, I 
placed a quantity of clay and flat stones in the vessel with a little water at the lowest 
part, in order to allow them to remain in the water or out of it. 
In a month the amputated limhs had undergone the reproductive process ; in one a 
miniature posterior extremity furnished with toes had been formed, in another the 
tail, and in fourteen days later the anterior extremity and the toes of the third were 
reproduced. 
I now began a series of experiments on the Frog (the Rana Temporaria) ; this 
batrachian being more manageable in regard to food, and arriving at its full deve- 
lopment in much less time than the Triton, the former only requiring about ten weeks, 
the latter about five months. 
I commenced my experiments and observations on the Frog in March 1848, ascer- 
taining accurately the influence of air, food, temperature and from the ovum to 
its full development. 
On the Influence of the Atmospheric Air. 
There are three modes of respiration in the tadpole of the Frog : — 1st, the Branchial ; 
2nd, the Pulmonary; 3rd, the Cutaneous. 
