434 
MR. HIGGINB'OTTOM ON THE INFLUENCE OF PHYSICAL AGENTS 
when the plant is in a state of decomposition, leaving the fibrous part. They gene- 
rally feed on the under part of the plant with the abdomen upwards, owing to the 
position of the mouth. 
I supplied the tadpoles with fresh water every third day, and with grass as often as 
necessary. In those vessels which were placed in the dark it was necessary to add 
grass more frequently, on account of the loss of the green colour it sustained in that 
situation. 
I observed they did not feed so well at a low temperature. The life of the tadpole 
cannot be preserved very long with fresh water and air alone without proper food. 
I placed a number of tadpoles in eight vessels, of which four were excluded from the 
light, and four exposed to the light in different degrees of temperature ; no food was 
put in any of the vessels after they had consumed the jelly. On the 11th of May, 
eight weeks and four days after the deposition of the spawn, the tadpoles remained 
very small, and the last of them died on that day. 
The jelly appears to be quite essential as nutriment to sustain the early life of the 
tadpole. Had they been deprived of it, they would have died at a much earlier 
period, as proved by my former experiment*. 
3. On the Injluence of Temperature. 
On the 11th of March 1848, 1 procured four round open earthenware vessels, each 
containing about three pints of water, and filled them about three parts full. In each 
I put a small quantity of the spawn of the frog just deposited, and I then placed them 
in four different degrees of temperature. 
The^r^^ was placed near the ceiling in a shaded part of a room, where the mean 
temperature was 60° Fahr., six or eight folds of black-glazed calico being tied over it 
so as to exclude all light. 
On the 20th of March (see Plate XXXIl.) the tadpoles left the ova ; on the 23rd the 
branchiae were fully formed ; on the 22nd of May the first was fully developed at a 
much earlier period than others placed in a lower part of the same room, exposed to 
the light at the mean temperature of 58° Fahr., and also earlier than in the pools. 
The second was placed at the same time in a situation where the mean temperature 
was 56°. On the 20th of March, nine days after the deposition of the ova, the embryos 
were lengthened, indicating the head, body and caudal extremity, and lay in a curved 
position within the ova. On the 25th some escaped from the ova. On the 28th the 
branchise were fully formed, and on the 6th of April they were absorbed. On the 
22nd of May the tadpoles had increased in size. On the 18th of August the first was 
fully developed. 
The third vessel was put within a larger one and placed in the open air, on a shaded 
* According to Mr. Brande (Philosophical Transactions for 1810), the jelly appears to be an intermediate 
substance between albumen and gelatine. 
