107 
and Structure of the Proteus Jnguinus . 
a little from one side of the abdomen to the other. So, in the 
siren, we see the trachea to open directly into the lungs, 
which, as in the above-mentioned larvae, says M. Cuvier, 44 sont 
deux longs sacs cylindriques, que splendent jusqu’ a fextremite 
posterieure de i’abdomen, et se replient meme alors en avant.” 
But, in the proteus, neither do the supposed lungs reach to the 
pelvis, nor does the supposed glottis open into the air-bladders, 
but issue in a cavity which communicates with the air-bladders 
by two long conduits. Thus, then, the structure of the bran- 
chial arches, the distribution of the bloodvessels, and the form 
and size of the lungs in the proteus, differ entirely from the* 
corresponding organs in the siren and larvae of the salamander. 
If, farther, we consider the mode in which frogs and sala- 
manders respire air, and compare it with that of the proteus, 
we shall obtain still farther evidence of the differences sub- 
sisting between them. All zoologists, including M. Cuvier, 
now admit that frogs first receive air into the mouth through 
the nostrils only, and from thence force it into the lungs by an 
action resembling deglutition. But neither the proteus nor the 
siren are able to respire in this manner ; for the nostrils in the 
former do not open into the mouth, but beneath the upper lip ; 
and in the siren, 44 les narines , simplement creusees sur les 
cotes du museau , ne penetrent point dans la houche says M. 
Cuvier. Neither do these animals respire air in the manner of 
serpents, for they are both destitute of ribs. When also the 
proteus takes air into the mouth, it escapes rapidly through the 
branchial apertures : nor is there any ground for believing that 
any portion of it enters the very narrow chink of the glottis to 
pass into its cavity, and from thence through the two mem- 
branous canals into the air-bladders. No muscular structure 
suited to produce such effects exists, and the fine membranous 
canals, subject to compression every instant from the stomach, 
altogether unfit them for performing the office of air- tubes of 
bronchi. In all reptiles that respire air, the structure of the 
organs is such as to permit free inspiration and expiration, how- 
ever different the form may be ; but in the proteus, the want 
of ribs and diaphragm, the fact that the nostrils do not open 
into the mouth, the extreme narrowness of the aperture termed 
glottis, and the narrowness, length, and compressibility of the 
