Hinckley.] 
310 
[January 4, 
They show this feature at the same stage of growth, that is, when 
the tadpole has reached the limit of its size. After the parts of 
the mouth are developed I have observed no change of form in 
the folds or papillae. 
In the tadpoles of Bufo americanus and B. fowleri one finds 
the least variability of mouth structure. Both have one fringed 
fold under the upper lip with a short gap above the upper jaw, 
and two fringed folds on the under lip with a space of fringe set 
in the edge of the border midway the lip. Some variability 
exists in the number of papillae at the edge of the lip and also 
in the number and exact position of those within the border. 
The mouth of B. fowleri is distinguished from that of B. ameri- 
canus (fig. 3) by a greater delicacy of texture, shown especially 
in the border papillae, which instead of being firm and rounded 
are soft and flat. The tadpoles agree in size and general form 
but differ in color. 
In the adult forms we find externally some difference in struc- 
ure but more in color, voice and habit. In Milton, B. americanus 
appears earlier in the spring, braving a lower temperature than 
B. fowleri. Usually the short period of egg-laying is over, the 
toads are silent and have dispersed to the land before B. fowleri 
is heard ; the latter remains longer at the water, the period of egg- 
laying extending into July. The bleat of B. fowleri with its far 
reaching metallic ring is usually heard after sunset. I have 
seen the latter give voice on the land, while the trill of B. ameri- 
canus, heard at all times of day and night during the mating 
season, I have only seen given in the water. 
The tadpoles of the Ranidae separate into two groups one 
having three and the other four fringed folds on the under lip. 
Those of R. silvatica, which represent the latter group, have a 
mouth (fig. 6) delicate in texture, with three fringed folds under 
the upper lip each side the upper jaw, decreasing in length 
towards the under lip. The fringe or teeth on the shortest fold 
are sometimes wanting. The edge of the upper lip is occasionally 
scalloped, and the fringed folds on the under lip which are varia- 
ble in length are usually wavy in such cases ; that next the under 
mandible or jaw is divided midway its length, and now and then 
the fold below it is partially separated at the same point. Occa- 
