82 SUPPLEMENT ON 



pletely as the rest of the body. Those on the lateral line are 

 distinguished from others by one or several little tubes passing 

 through them, and often by other particularities. There are 

 also instances of the scales forming the lower edge of the 

 belly, being compressed, sharp, and in their arrangement 

 presenting a kind of external sternum, resembling a saw, as 

 may be seen in herrings and serra-salmons. The kind of 

 teguments furnished by scales is very proper for protecting 

 the animal against the shocks and frictions to which it is 

 exposed, and for facilitating natation ; but offers little protec- 

 tion against changes of temperature. Fishes are, however, 

 less sensible of cold than birds or quadrupeds, because the 

 temperature of the surrounding medium is about equal to 

 their own. 



The organs of nutrition of fishes are analogous to those of 

 other vertebrated animals : they take and divide their food 

 with the teeth ; it is subjected to a first digestion in the 

 stomach ; thence passing into the intestinal canal, it is im- 

 pregnated with the bile discharged from the liver, and 

 usually also with a liquid like that of the pancreas ; the 

 nutritive juices, absorbed by vessels analogous to lacteals, 

 and perhaps also in part by a direct action of the veins, are 

 mixed with the venous blood, carried to the heart, and thence 

 to the branchiae, where the contact of the ambient element 

 converts the mixed fluid into arterial blood, which then pro- 

 ceeds to nourish the whole system : some parts of it are, how- 

 ever, carried off in transpiration, in the form of liquids oozing 

 through the skin, and finally by the reins and urinary appa- 

 ratus. We must therefore say a few words relative to the 

 organs of manducation, digestion, circulation, respiration, and 

 of the excretions. 



Manducation and teeth. We have already shown how 

 fish seize their prey and swallow it ; this being chiefly per- 

 formed by means of the teeth, it is proper to notice them 



