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tions imitate those of the waves of the sea, A pretty 

 thin membrane lines _the inside cf the shell, and some- 

 times the outside. It is a kind of mantle, furnished 

 with trachea, or air-vents, which separate the air from . 

 the water ; at the origin of which are perceived, little 

 gills, destined to the same uses. The heart, which is 

 situated near the surface of the body, has a sensible 

 motion, whereby it raises and falls alternately. In tLe 

 conchae, it is underneath the stomach. 



ip. Animals with shells bear an affinity to iiskes, 

 Reptiles seem to take place between, or next to them j 

 being united to shelled animals by the slug, and to the 

 fishes by the water-serpent. 



In reptiles, animal perfection begins to increase in a 

 sensible manner. The number of their organs, their 

 conformation and exercise, give them, on this account, 

 a greater analogy with the mechanism of those animals 

 w esteem the most perfect. The organs of vision, 

 hearing, and circulation, furnish examples sufficient to 

 indicate this. This analogy is augmented in fishes, 



The eel, by its formation, and creeping fishes, by 

 their method of moving, connect fishes with the water- 

 serpent. 



20. Fish, like reptiles, are for the most part covered 

 with scales, whose figure, and rich colours, help to make 

 a distinction between the species. 



There is a great variety in the form of fishes. Some 

 are long and slender ; others are broad and short. We 

 see among them, flat, cylindrical, triangular, square, 

 and circular ones. Some are armed with a great horn* 

 Others wear a. long sword; or a kind of saw. A third 

 sort are furnished with pipes, through which they throw 

 out the remainder of the water they have swallowed. 

 Wings are to birds, of the same use as Jins to fishes. 

 E 5 



