140 



THE SNAIL. 



part of the subject, a few of the principal points may 

 be explained, serving to show the plan pursued, and also 

 the marvellous resources, not of nature, but of nature's 

 God, whose wisdom and power are alike incomprehen- 

 sible. 



Let us, then, take one of the air-breathing gasteropoda, 

 for instance, the common snail. If we watch it crawling 

 along, its body being protruded from the shell, we may 

 observe on the right side of the body, near the margin 

 of the shell, a circular orifice : this is the mouth of a 

 breathing tube, and it leads to a capacious chamber on 

 the back of the animal, above the visceral cavity, and 

 separated from it by a partition. The roof of this 

 cavity is lined with a network of blood-vessels, of ex- 

 quisite delicacy and most beautifully disposed, and in 

 these the blood undergoes the purifying influence of the 

 air. The muscular floor of this cavity, already noticed, 

 is the agent by which the air is drawn in and expelled, 

 by a series of alternate movements, analogous to those 

 of the diaphragm of quadrupeds. Hence, Cuvier has 

 given to these animals the title of Les pidmones, or 

 Pulmobranckiata, that is, having their branchiae like 

 lungs ; and the similarity is very remarkable. 



Leaving these mollusks, we come to the first of the 

 aquatic orders, which Cuvier terms Les 7iudibranches, or 



