their organization, the varied instincts and habits with which they are endowed, their means of offence and defence, and the great diversity of form and structure which they exhibit, as rich a feast of intellectual gratification to the philosophic student of Nature, as any other of the wonderful works of God. In this last respect the Class of Reptiles is eminently worthy of attention. "In Mammalogy and Ornithology, we find that the animals which are treated of under those branches are respectively formed according to one leading type, which, however modified, may be traced throughout the whole chain of beings with which those branches of Zoology are conversant. From an Elephant to a Mouse, from a Whale to a Porpoise, the same uniform principle of construction may be recognised. The same principle of organization governs the conformation of an Ostrich and a Humming-bird. But in Herpetology, we have various types or principles of structure. Not to dwell upon the more obvious differences in the organization of a Tortoise and a common Snake, we shall find in more cognate creatures, the Saurians for example, a striking variation in structure. The skeleton of a Crocodile differs widely from that of a Chameleon; . . . and how widely are these again separated from the Frogs and Toads!"* * Penny Cyclop. xix. 403. In one respect in which Reptiles agree among themselves, they agree also with the Classes of Birds and Fishes; the reproduction of their species is effected by means of eggs. For the most part these are encased in a calcareous covering, either hard and shelly as in the Tortoises, Crocodiles and some Saurians, or tough and leathery as in most of the Serpents: in the Amphibia, however, they are destitute of any covering. In a few instances, the young are brought forth alive; but these are rather apparent than real exceptions to the general rule, the eggs in such cases being hatched in the body of the parent, or ruptured in the act of deposition. Our native smaller Lizard, Viper, and Slow-worm, afford familiar examples of this peculiarity. Reptiles do not in general incubate their eggs; but there is reason to believe that the Boas and Pythons are exceptions to this rule. The heart in this Class is so constructed that at every pulsation only a part of the blood from the system is thrown into the lungs, the remaining portion returning into the circulation without being aërated. As animal heat is derived from the communication of oxygen to the blood, in its exposure to the air when passing through the lungs, it follows that the imperfect aëration of the blood in these animals is attended with a diminution of vital heat, and that they are what is called cold-blooded; in other words, the heat produced by respiration is so small, that the difference 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 Dragons, and the flying of the Pterodactyles, there is hardly any mode of animal progression which is not to be found among the Reptiles."* The temperature of the blood does not require that the body should be clothed with a substance, such as hair or feathers, which might resist the abstraction of animal heat. Hence the skin is either quite naked, as in the Amphibia, or covered with a sort of mail, composed of plates or scales, for defence. It is in the warmer regions of the globe that Reptiles most abound; both as to the number of species, and of the individuals which constitute them. There also they display the greatest variety of form and colour, the most gigantic bulk, and the highest amount of animal energy. The few species that inhabit temperate and cold countries, commonly retire into concealment and become torpid on the approach of winter. Yet it has been remarked that they can more easily bear the rigour of a severe winter, than suffer the want of a hot summer. "It is interesting to remark the manner in which, according to Berghaus, the number of species diminishes as we pass from the sunny regions of the East to the duller and more cloudy climes of Western Europe. Thus Italy with her islands can number forty-seven species; France has thirty-one; * Penny Cyclop. xix. 410. |