covering. In general, they are enveloped in a transparent glaire or jelly.
The organization of the skeleton, as well as other peculiarities in the anatomy, manifest that the Amphibia are formed on a grade of structural development, inferior to that of the Enoplia. The skull is united to the spine by two processes,
SKELETON OF FROG.
or condyles, instead of one, the ribs are either rudimentary or altogether wanting, and the sternum or breast-bone is imperfectly developed, or absent.
“To any person,” observes Professor Bell, “capable of appreciating the interest attached to the study of physiological phenomena, the contemplation of an animal, which, at one period of its life, is endowed exclusively with the organs of aquatic respiration, resembling the gills of fishes, with means of locomotion adapted only to a con-
