LECTURE VII. 
5 
or bears so great a proportion to the vesicular 
one, or that of the air-cells, that the latter are 
scarce distinctly visible without a close and minute 
survey ; but on the contrary, in the Amphibia the 
vesicular system greatly preponderates over the 
vascular, insomuch that in some of the tribe, as 
in the Tortoises for instance, the lungs seem to 
consist almost entirely of bladders or vesicles, 
while the blood-vessels distributed through them, 
and constituting their vascular system, appear 
very slight in comparison. In Frogs the difference 
is still more striking ; for in these animals the 
lungs, when in a state of inflation, exhibit the ap- 
pearance of a pair of bladders, the internal part 
or cavity of which is slightly subdivided into nu 
merous cells, reaching but a little way down, or 
in such a manner as to leave a large central va- 
cuity in each lobe of the lungs ; while the blood- 
vessels are distributed in a very elegant and beau- 
tiful manner between them. In many of the 
Lizards the lungs seem even less complex than in 
the Frogs; for in some of the smaller Lizards, 
and particularly in the common Water-Newt, or 
L. aquatica of Linnseus, the lungs are merely a 
pair of lengthened bladders, without any internal 
