260 



lamella, from whence it returns by veins which dis* 

 tribute it throughout the body. 



6. In most fishes tho heart is like that in other 

 animals. But in some it has only one ventricle ; 

 which necessarily occasions a difference in the manner 

 wherein the blood circulates. In some also the 

 blood is not red, but clear and transparent. In others, 

 especially shell-fish, besides the arteries and veins, 

 there are open tubes, which convey the water to the 

 farthest part of them ; probably that they may find 

 no want of water, when they continue some time on 

 shore. 



7. The air-bladder is described as a bag filled with 

 air, sometimes composed of one, sometimes of two, 

 aud sometimes of three divisions, situated towards the 

 back of the fish, and opening into the maw or the 

 gullet. It is commonly supposed, by its swelling at 

 the will of the animal, to increase the surface of the 

 fish's body, and so to enable it to rise to the top of 

 the water, and keep there at pleasure- On the con. 

 trary when the fish wants to descend, it is supposed 

 to empty this bladder of its air, and to sink to the 

 bottom. 



But many fishes have an air bladder, that conti- 

 nually crawl at the bottom ; such as the eel and 

 the flounder : and many more are entirely without it, 

 that swim in every depth ; such as the anchovy and 

 the fresh. water gudgeon. Indeed, the number of 

 fishes that want this organ is alone a sufficient proof 

 that it is not accessary for the purposes of swimming ; 

 and the ventral fins, which in all fishes lie flat upon 

 the water, are fully sufficient to keep them at all depths. 



8. The stomach is, in general, placed next the 

 mouth, and though not sensibly hot, is endued with 

 a surprising faculty of digestion. Its digestive power 

 seems in soui measure to increase with the quantity 



