OF NEW ENGLAND. 15 
central denticle, flanked on each side by forty-four lateral 
denticles. There were one hundred and twenty-three 
transverse rows, making the whole number of denticles 
onthe membrane ten thousand nine hundred and forty- - 
seven, or, about eleven thousand. The form, and number 
of denticles in each species vary, as we shall show here- 
after. 
In looking for the breathing hole of the snail, those 
ignorant of its structure might refer to the mouth as the 
opening through which it inhaled air. It is a common 
idea that insects breathe through the mouth, because the 
higher animals do so. Now insects breathe through little 
perforations on the sides of their body, and the snail has 
an aperture on the right side of its body, just within the 
aperture of the shell, through which it breathes. This 
aperture can be plainly seen in the mantle or skin which 
fills the mouth of the shell, (Fig. 11, a, Plate 1) by turn- 
ing the snail over. The lung is a simple cavity, lined 
with a net work of blood vessels. The blood is a bluish 
colored fluid, and is circulated through the body and lung, 
by a pulsating heart composed of two chambers,.an auri- 
_ cle-and a ventricle, separated by a double valve. -The 
heart’s pulsations can be distinctly seen through the lower 
part of the translucent shell of many species. Fig. 2, h, 
plate 1, represents the heart situated in the pulmonary 
sot In this figure the lung is represented as 
k from the animal, exposing the heart. Fig. 12 repre- 
sents the heart and lung of a common fuy. It would 
lead us too deep into the anatomy of the mai, were we 
to indicate the character and position of the liver, kidney, 
and many other organs which combine to make up the 
complicated structure of our apparently simple snail. Suf- 
fice it to say, that however insignificant many of the lower 
