640 REPTILES AND AMPHIBIANS. 
only by diminishing its cavities but by expanding its own. In this 
manner the deep meshes sometimes appear white while the exterior net- 
work takes on a pearly aspect. The animal in this manner, by blend- 
ing in a different degree two or three primitive colors, changes its shade 
so much that it comes to resemble the object upon which it happens to 
be. A similar power to vary these colors at willis present to a greater or 
less extent in all the Hylide. The advantages of this, in enabling these 
animals to escape their enemies, and to approach their prey unobserved, 
is too obvious to be considered here. 
In this connection it may be mentioned, that tadpoles sometimes show 
a mimetic coloring. A case of this kind is recorded by Miss Monk,* 
in which, being kept in an aquarium with Water Purslane, Ludwidgia 
palustris, they imitated almost precisely the color of the leaves. So per- 
fect was the resemblance that a friend visiting her was actually deceived 
and mistook aleaf foratadpole. Personally I have seen such cases of imi- 
tation, but none sufficiently marked to justify a person being misled in 
this manner. 
Again, the serpents have a remarkable power of enlarging their 
bodies by the inhalation of air. To understand how this is done it is but 
necessary to dissect a snake, and observe the situation and length of the 
lungs. By thus enlarging his hody the serpent renders himself more 
formidable in appearance, and has thus a tendency to frighten away an 
enemy. Add tothis the peculiar blowing sound with which the air is 
emitted, sometimes as in Heterodon, suggesting the rattle of the Crotalide, 
and again, as in Pityophis, said to imitate the roaring of a bull,and this 
matter of exhalation, as well as inhalation, has a profound significance. 
Another mode of protection is in the secretion of some of these ani- 
mals. Thus the frog on being caught usually ejects a quantity of fluid, 
and also becomes more or less swollen. The use of this ejection was to 
me a mystery until seeing Mr. Aldrick’s} account of a snake gliding 
upon a frog, when the latter simultaneously jumped and threw this 
liquid into the mouth and eyes of the serpent. The latter was ap- 
parently blinded by the discharge, sprung wildly from side to side, and 
lost track of hisintended prey. This incident seems to indicate that the 
ejection of this fluid in the frog accomplishes the same purposes as the 
discharges in the Bombardier Beetles, and enables the Batrachian to 
escape its enemies. 
However this may be, the cutaneous secretions of some Reptiles, 
and Amphibians are admirably adapted to the purpose of protection. 
*Am. Naturalist, vol, xii, p. 695. 
+t Am. Naturalist, vol. xii, p. 473, 
