Bz THEPHILOSOPHY 



urinary bladder, which lies in the lower part of the abdomen, and 

 the urethra terminates in the anus. 



Fifhes have a membranous diaphfagm, or inidiifF, that forms s 

 fack in which the heart is contained. The heart is of a triangular 

 figure. It has only one auricle, one ventricle, and one great artery. 

 This artery, inftead of fupplying all the parts of the body, as in the 

 frog, is diftributed entirely on the gills. All the branches terminate 

 there, and become at laft fo fmall that they efcape the naked eye. 

 The branchiae, or gills, lie in two large flits on each fide of the head, 

 and are analogous to the lungs of land-animals. The figure of the 

 gills is femicircular, and on each fide of them are immenfe numbers 

 of fibrils refembling fringes. The gills are perpetually fubjeded to 

 an alternate motion from the prelTure of the water and the adlion of 

 the mufcles. They are covered with a large flap, which allows an 

 exit to the water neceflarily taken in by the animals every time their 

 mouths are opened. The blood is again colleQed by a vafl: number 

 of fmall veins, which, inftead of going back a fecond time to 

 the heart, immediately unite, and form an aorta defcendens, which 

 fends off branches to fupply all the parts of the body, except the 

 gills. From the extremities of thefe branches the blood is colieded 

 by veins, and returned to the heart nearly in the fame manner as in 

 other animals^ 



The organs by which the nutritious part of the food of fiflies are 

 extratfled and conveyed to the general mafs of blood, and known 

 by the names of ladeal, abforbent, and lymphatic veflels, are fo ana- 

 logous to thofe of men and quadrupeds, that it is unnecefl"ary to de- 

 fcribe them. For the fame reafon, no defcription fliall be given of 

 the nerves, which, as in other animals, proceed from the brain and 

 fpLnal marrow, and are dlftributed over every part of the body. 



Having; 



