FROGS. 305 
bladder so tightly over the animal’s head that it could not obtain 
any air by way of the nostrils. The creature was then sunk 
under some water placed in a vessel, and when, after the lapse of 
an hour or two, this water was carefully examined, it was found 
to contain a considerable portion of carbonic acid gas. Frogs, 
with their heads enveloped as described, have been known to live 
under stagnant water, which was periodically changed, for at least 
ten weeks, and to die as soon as the water was allowed to remain 
unrenewed. A Frog, so bandaged, lived for twenty days in a 
damp atmosphere, and other Frogs existed for from thirty to 
forty days when deprived of their lungs by excision. On the 
other hand, experiments have tended to prove that Frogs cannot 
exist for any lengthened period when deprived, in the matter of 
respiration, of the assistance of the skin. For example, they 
cannot live in a perfectly dry atmosphere, nor when their skin is 
coated with some non-porous substance. 
In order that the cutaneous respiration may be effectively 
carried on, the very sensitive skin of the Frog must be kept 
moist. Most people who have caught Frogs at any time will have 
noticed that they are apt to discharge from their body a clear, 
colourless fluid. They may do this under the influence of fear, or 
that, being relieved of the weight of the liquid, they may be the 
better able to escape. This fluid, the late Mr. Thomas Bell said, 
in his book on “‘ British Reptiles,’”? comes from a_ portable 
reservoir, which is provided for the purpose of supplying the 
necessary moisture to the skin of the Frog whenever it happens to 
be at some distance from water or dampness. The reservoir, 
which, he says, has been mistaken for the urinary bladder, is 
filled, according to him, by the absorption of water by the 
skin, and which can again be absorbed by the skin when 
it needs moisture. 
(8) In many species of Frogs the males possess one sac or a 
pair, situated near the throat or on each side of the head. By 
means of these sacs the animal is able to make the noise which is 
commonly called croaking or roaring. These sounds are gener- 
ally heard in spring-time. 
(9) The leg of a Frog has in its thigh and calf a great 
resemblance to those parts of man. 
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