INTRODUCTION. 639 



attention has not hitherto been properly directed, is the various modes 

 of protection furnished them by nature. We find the Turtles, for the 

 most part, provided with a union of the cuticle and skeleton into which 

 they can retreat, and which can be closed about them. To see the value 

 of this mode of protection, it is but necessary to endeavor to draw out the 

 head of one, which will be found to be a very difficult task. In a similar 

 manner, the scales, plates, and spines, so common as a dermal covering, 

 have a profound significance, and their color is a matter of too great a value 

 to be overlooked. The Rattlesnakes and Copperheads are provided with 

 fangs, for injecting venom, and the former with a caudal rattle, by the 

 vibration of which it may aid in frightening away its foes. But the color 

 has an important bearing. The young of the venomous Oroialophorus 

 Urgeminvs, and of the harmless Tropidonotus sipedon and Ophiholvs triangulus, 

 bear such a resemblance to each other that it might be considered a case 

 of mimicry. However, the color of these animals is more or less adapted 

 to their surroundings. The Green Snake resembles closely the grass 

 through which it crawls, and the same is true also of the Storerias and 

 Striped Snakes. Unless closely examined they could easily escape the 

 eye of the observer. In like manner the markings of frogs furnishes an 

 excellent illustration of adaptation. The green of the Bull -frog and the 

 spots on the Leopard Frog need but be mentioned to be appreciated. 

 Rana temporaria var. sylvcdica^ when pursued, conceals itself in grass or 

 leaves, which it resembles so closely as to be discovered with difficulty. 

 The Common American Toad (Bufo americanus), might not at first seem to 

 have its colors most suitable for protection, and yet when we see it in its 

 secluded retreats, under stones and in odd corners, and consider its noc- 

 turnal habits, the conviction forces itself upon me, that probably no 

 better shades could have been chosen. As desert animals are sand colored, 

 and arctic are white, like the snow, so these animals show a decided 

 adaptation to their surroundings. 



The best illustration is furnished by the common Tree Toad .(Hyla ver- 

 sicolor). Like the Chameleon, this little animal can change its color, and 

 thus transform itself into a being resembling the limb or branch on 

 which it sits. As Milne Edwards* found in the Chameleon, so in this 

 there are two sets of cutaneous glands, the one superficial and the other 

 deep. The former of these gives it a green coloration, with a golden re- 

 flection; the latter are much thicker and dark. They contain many 

 brush-shaped cavities, and the expansion of these towards the circum- 

 ference determines the color and causes the green tint to disappear, not 



*Ann. dee Sci. Nat., 1834, p. 46. 



