Page:Natural History, Reptiles.djvu/12

4 between the temperature of their bodies and that of the air or water in which they live, is not sensible to the touch. The Sub-class Amphibia, including the Frog-like Reptiles, pass through a sort of metamorphosis, breathing by means of gills in their early stages; and there are a few which have both gills and lungs through their entire existence.

The senses are in general well developed, though in various degrees in the different Orders: in some, however, the sense of sight appears to be nearly obliterated, as in Typhlops, and in Proteus. Their brain is comparatively small; and their sensations seem less referrible to a common centre, than in the higher Classes: life, and even voluntary motion, continues long after the brain is removed; the irritability of the muscular fibre is preserved for a considerable time after separation from the rest of the body; and the heart pulsates for many hours after it has been detached.

“The motion of Reptiles is as various as their structure, and exhibits a great diversity, particularly in the modes of progression. The slow march of the Land Tortoise, the paddling of the Turtles, the swimming and walking of the Crocodiles, the Newts, and the Protei, the agility of the Lizards, the rapid serpentine advance of the Snakes, the leaping of the Frogs, offer a widely extended scale of motion. If we add the vaulting of the