ON THE DEVELOPMENT OF THE TRITON AND THE FROG. 
435 
side of a house, and entirely covered with wood, so as to exclude all light, the mean 
temperature being 53° Fahr. 
March 20th. — In nine days after the deposition of the ova, the embryos retained 
their globular form, but considerably increased in size. 
On the 25th they had the elongated form within the ova ; on the 31st they escaped. 
On the 4th of April the branchise were fully formed, and on the 11th they were 
absorbed. May 22nd, the tadpoles were increased in size. On the 28th of August 
the first was fully developed (see Plate XXXII.). 
The fourth vessel I placed in the rock-cellar. The temperature was uniformly 48° 
Fahr. from the 11th of March to the 15th of May, 50° to 54° Fahr. from May 15th 
to July 6th, and 55° Fahr. uniformly from July to October 31st. 
March 31st. — The tadpoles escaped from their ova on the same day as in that in 
the open air, the temperature being in the cellar uniformly 48° Fahr., in the open air 
53° mean temperature. 
On the 6th of April the branchise were formed, and on the 18th they were absorbed. 
On the 22nd of May the tadpoles were very small, but from that period to the 5th of 
September they grew much more rapidly. On the 31st of October the first was fully 
developed. 
It will be observed (Plate XXXII.) that when the tadpole in the room was fully 
developed at the mean temperature of 60° Fahr., those in the open air were small at 
the mean temperature of 53°, but those in the cellar were smaller still, having been 
influenced by the low temperature of 48°; from March 11th to May 6th, when the 
temperature became constantly 55°, they advanced more rapidly in size until their 
full development. 
November 17th. — Soon after this period the temperature in the rock-cellar was 
from 50° to 54° Fahr. for a month, and during that time there were no more tadpoles 
fully developed. One of them had three legs only ; for upwards of three weeks the 
fourth leg could be seen distinctly under the skin when the animal moved, but it did 
not protrude. 
All these results are displayed in Plate XXXII., in which the difference of tem- 
perature and its effects are registered. 
4. On the Influence of Light. 
With regard to the question of full development of the tadpole of the Frog in the 
absence of light, I am enabled by the most minute observation to state that it ad- 
vances in growth equally well in the dark and in the light, and that absence of light 
has therefore no influence in retarding its development. 
I have ascertained this by frequent experiments during the last two years ; one ex- 
periment was made on an extensive scale. 
I had six vessels with tadpoles, three exposed to the light in different degrees of 
temperature, and three from which the light was excluded. 
3 K 2 
