IO REPTILES AND BIRDS. 
upon their mode of respiration, the volume of their eggs, and their 
colour. 
Numerous systems have since appeared in France, Germany, 
and England; but we shall best consult the interest of our readers 
by briefly describing the classification adopted by Professor Owen, 
the learned principal of the British Museum, in his great work 
on the vertebrata. 
The two great classes Batrachians and Reptiles, include a 
number of animals which are neither clothed with hair, like the 
Mammalia, covered with feathers like the Birds, nor furnished 
with swimming fins like Fishes. The essential character of Reptiles 
is, that they are either entirely or partially covered with scales. 
Some of them—for instance, Serpents—move along the ground 
with a gliding motion, produced by the simple contact and ad- 
hesion of the ventral scales with the ground. Others, such as 
Tortoises, Crocodiles, and Lizards, move by means of limbs; but 
these, again, are so short, that the animals, with very few exceptions, 
appear only capable of crawling slowly. Again, some of this class 
are only furnished with feet in the pectoral region; but this is the 
exception. The locomotive organs in Scrpents are the vertebral 
column, with its muscles, and the stiff epidermal scutes crossing the 
under surface of the body. “A Serpent may, however, be seen to 
progress,” says Professor Owen, ‘without any inflection, gliding 
slowly and with a ghost-like movement in a straight line; and if the 
observer have the nerve to lay his hand flat in the reptile’s course, 
he will feel, as the body glides over the palm, the surface pressed as 
it were by the edges of a close-set series of paper knives successively 
falling flat after each application.” In some, as in various Lizards, 
the limbs acquire considerable strength. 
There is one genus of small Lizards, known as the Dragons (Draco), 
whose méans of progression present an exception to the general rule. 
Besides their four feet, these animals are furnished with a delicate 
membranous parachute, formed by a prolongation of the skin on the 
flanks, and sustained by the long slender ribs, which permits of their 
gliding through the air upon their prey from a considerable height. 
Batrachians, again, differ from most other Reptilia by being 
naked; moreover, most of them undergo certain metamorphoses. 
In the first stage of their existence they lead a purely aquatic life, 
and breathe by means of gills, after the manner of fishes. Young 
Frogs, Toads, and Salamanders, which are then called ¢adpoles, have 
at that stage no resemblance whatever to their parents in structure. 
They are little creatures with slender, elongated bodies, destitute of 
