VOL. XIX.] PHILOSOPHICAL TRANSACTIONS. 13p 



The heart of a fish is difFerent from that of other animals in its having only 

 one ventricle ; for it has only the vena cava and the aorta that open into 

 it, having no lungs ; so that by the aorta the blood comes out of the heart 

 which is branched into a thousand capillaries over the bronchia, and is after- 

 wards reunited ; which reunion is made under the basis of the cranium ; and 

 because the blood, when once there, has no need of being forced higher upwards, 

 they have no occasion for a second ventricle for that purpose, as terrestrial 

 animals have. The reunion of these capillaries of the bronchia being made, 

 they form two large trunks, of which one proceeds towards the head, and the 

 other towards the lower parts. 



Fish have a diaphragm, but not for the same purpose as in other animals that 

 breathe ; it is always straight and tense, and perpendicular on the vertebrae. 

 Their stomach is membranous : for fish swallow down other small fish whole, 

 and sometimes earth ; therefore it is necessary to have a power of contracting 

 itself forcibly to break in pieces its contents.* Their intestines make several 

 great windings, a sign the fermentation is but slow in them, which is made up 

 by their great length. 



The liver has much the same situation as in other animals, as also the spleen : 

 they are provided with a gall bladder, a ductus choledochus, and pancreas, or 

 rather two little bags fastened to the ventricle for the same use ; they have in- 

 deed usually many pancreases, so that in some there have been found 44 ; they 

 have kidneys, bladder, &c. They have the ovary near the vertebrje of the 

 loins ; the eggs come out at a passage below the anus, and the male has a like 

 ductus or hole, by which they eject their seed upon that of the female, to im- 

 pregnate the eggs, of which the male sometimes changes the colour as he 

 passes over them, when he casts his seed upon them after they are laid. 



Fish have on the vertebras of the loins a bladder, very large in proportion to 

 their bulk, which serves, by dilating or compressing itself, to render the fish 

 lighter or heavier, as occasion requires, for swimming. And if this be by any 

 means hurst, so that it cannot be extended, the fish can no more raise itself in 

 the water, but keeps continually at the bottom. Tiie fins and tail assist them 

 in their passage through the water : but it is this dilatation of the air in the 

 bladder that makes them capable of swimming, after the same manner as the 

 dilating of the lungs and thorax of a man bears him up in the water. Flat fish, 

 such as soles, have none of this bladder : for they are able, by reason of their 

 breadth, to sustain themselves in the water. Craw-fish and other shell-fish 



* Their digestion is performed, not by trituration, or mechanical force, but by chemical solution, 

 viz. by the dissolving action of the gastric juice. 



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