130 
COMPARATIVE ANATOMY. 
teeth, could be answered by an instrument which had none 
of these; could be supplied, and that with many additional 
advantages, by the hardness, and sharpness, and figure of 
the bills of birds. 
.Everything about the animal mouth is mechanical. The 
teeth of fish have their points turned backward, like the 
teeth of a wool or cotton card. The teeth of lobsters work 
one against another, like the sides of a pair of shears. In 
many insects, the mouth is converted into a pump or gucker, 
fitted at the end sometimes with a wimble, sometimes with 
a forceps; by which double provisions, viz. of the tube and 
the penetrating form of the point, the insect first bores 
through the integuments of its prey, and then extracts the 
juices. And, what is most extraordinary of all, one sort of 
mouth, as the occasion requires, shall be changed into an¬ 
other sort. The caterpillar could not live without teeth; 
in several species, the butterfly formed from it could not 
use them. The old teeth therefore, are cast off with the 
exuviae of the grub; a new and totally different apparatus as¬ 
sumes their place in the fly. Amid these novelties of form, 
we sometimes forget that it is, all the while, the animal’s 
mouth; that, whether it be lips, or teeth, or bill, or beak, 
or shears, or pump, it is the same part diversified: and it 
is also remarkable, that, under all the varieties of configura¬ 
tion with which we are acquainted, and which are very 
great, the organs of taste and smelling are situated near 
each other. 
III. To the mouth adjoins the gullet: in this part also, 
comparative anatomy discovers a difference of structure, 
adapted to the different necessities of the animal. In 
brutes, because the posture of their neck conduces little 
to the passage of the aliment, the fibres of the gullet, which 
act in this business, run in two close spiral lines, crossing 
each other: in men these fibres run only a little obliquely 
from the upper end of the oesophagus to the stomach, into 
which, by a gentle contraction, they easily transmit the 
descending morsels; that is to say, for the more laborious 
deglutition of animals, which thrust their food up instead 
of down, and also through a longer passage, a proportion- 
ably more powerful apparatus of muscles is provided; more 
powerful, not merely by the strength of the fibres, which 
might be attributed to the greater exercise of their force, 
but in their collocation, which is a determinate circum¬ 
stance, and must have been original. 
IV. The gullet leads to the intestines; here, likewise, 
as before, comparing quadrupeds with man, under a gene- 
