STRUCTURE OF SERPENTS AND BATRACHIA. 97 
gullet, ce, which leads from the mouth to the stomach, is a 
long and very wide canal, being even larger than the stomach 
at its commencement; a portion of it is removed at ce', in 
order to show the heart, &c., which would otherwise be con¬ 
cealed by it. The stomach, i, is long and narrow; and the 
intestinal tube, i', after making a few turns or convolutions, 
passes backwards in a straight line, to terminate in the cloaca, 
cl, which opens externally by the orifice, an. The liver, /, is 
also much lengthened. From the mouth also proceeds the 
long windpipe, t t, which conveys air to the lungs, or rather 
to the single lung; for the lung on the left side, p', is scarcely 
at all developed, whilst that on the right, p, extends along a 
great part of the body. At o is seen the ovarium, in which 
the eggs, o' o', are produced; and this also is very much 
lengthened, extending from the cloaca a good way up the 
body, so as nearly to meet the lung. The other references 
are to the parts of the heart, and the principal vessels; the 
structure and arrangement of which will be explained here¬ 
after (§ 284). 
86. The Batrachia, or animals of the Frog tribe, are 
readily distinguished from all the preceding, by their soft 
naked skins; even when the form of the body, as in the com¬ 
mon Salamander or Water-Newt, resembles that of the lizards. 
They are also remarkable for the metamorphosis which they 
undergo in the early part of their lives : for they come forth 
from the egg in a condition which is, in all essential particu¬ 
lars, that of a fish, and undergo a gradual series of changes, 
by which their form and structure become assimilated to those 
of the true reptiles. This change is most complete in the 
Frogs and Toads; the early form of which is known as the 
tadpole . The principal stages of this change are represented 
in figs. 35 to 39; in which, however, the relative sizes are 
not preserved, the tadpoles being much larger in proportion 
(for the sake of displaying their form and the gradual 
development of their legs) than the complete frog. Soon 
after the young tadpole has come forth from the egg, it pre¬ 
sents the form which is shown in fig. 35 ; its head and 
trunk are large, and the latter is prolonged into a flattened 
tail, by which the little animal swims freely through the 
water. There is not the least appearance of limbs or mem¬ 
bers. It breathes by gills, which are long fringes, hanging 
H 
