ON THE DEVELOPMENT OF THE TRITON AND THE FROG. 
433 
In the branchial state the body of the tadpole is very small, and at this period they 
flock to the sides of the vessel in which they are contained close to the edge of the 
water, nearly exposing the branchiae to the atmospheric air, the lungs being as yet 
unemployed. 
About a fortnight before the metamorphosis of the tadpole into the frog, its body 
is very large, and the cutaneous surface for respiration, including the tail, is very con- 
siderable ; but when the development takes place, the body of the frog is again small, 
and there is not a sufficient surface for respiration, so that if the animal continues in 
the water, it becomes asphyxiated. Life then depends more on the pulmonary than 
the cutaneous respiration. 
I found that the tadpole of the Frog soon dies in either aerated or boiled water if 
excluded from atmospheric air ; those in aerated water live the longest ; some of them 
I found at the top of the water, and on examination the lungs were observed to be 
inflated, whilst those tadpoles in the boiled water sank to the bottom of the vessel. 
Tadpoles put into boiled water exposed to the atmospheric air live as in aerated 
water. 
2. On the Injiuence of Food. 
The food of the tadpole is derived from two sources. The first is the gelatine of 
the ova, the second the plants growing in the water in which they are deposited. 
1848. — On the 11th of March I put some spawn of the frog, newly deposited, into 
eight shallow earthenw'are vessels containing water; in four of them I added grass 
and duck-weed to serve as food for the future tadpoles, in the other four 1 put none. 
I observed in all the vessels that the tadpoles, after escaping from the ova, had about 
an equal growth, as long as any of the jelly-like substance of the ova remained ; but 
after that was consumed, the tadpoles in the vessels where there was no grass were 
promptly retarded in their growth. 
April 17th. — To prove whether the jelly of the ova was food for the young tadpoles, 
I separated a number from the jelly, putting the tadpoles in one vessel with water, 
and the jelly in another. 
In thirteen days I found the tadpoles had not increased in size, and that some of 
them were very weak and nearly inanimate. On this day I placed them all with the 
jelly. In seven days the jelly was consumed, and some of the tadpoles had nmch in- 
creased in size, others of them had died from having been so long and at so early a 
period deprived of their^r.y^ food. 
After the tadpole has finished feeding on the jelly, nothing more is required for 
food than grass and duck-weed, the grass serving for food, the duck- weed both for 
food and as a shelter, and also probably yielding its influence as a living vegetable 
in the water. The grass is sufficient as food to produce the full development of the 
tadpole, which feeds upon the chlorophyle which adheres to the cells of the plant, 
3 K 
MDCCCL. 
