GENERAL REMARKS ON FISH. 51 



on the animalculge retained in the passage of the water 

 through their gills. 



Shad caught in the salt water of the Chesapeake Bay and 

 brought to this city, have been found with small fish in their 

 stomachs, but they were of species known only in salt water. 

 All fish are more or less omnivorous. I have opened Eock- 

 fish, which are known to be predatory in their habits, and 

 found the tender shoots and stalks of aquatic grasses in the 

 throat and pouch. 



The fish which furnish sport to the angler, have generally 

 eight fins ; two pectorals, two ventrals, one anal, two dorsals, 

 and one caudal. 



The pectorals, as the term implies, are the breast fins, and 

 project from the humeral bones ; they are homologous to the 

 arms in man, or the fore legs of quadrupeds. The ventrals, 

 named from being attached to the belly, in most spine-rayed 

 fish, are immediately or nearly under the pectorals ; in soft- 

 finned fish, about midway between the head and tail. The 

 anal is immediately behind the vent ; the dorsals on the 

 back ; and the caudal, which is generally called the tail, is 

 the hindmost fin. This last fin is the chief motor ; it is used 

 as an oar in sculling, and acts also as a rudder : the dorsals 

 and anal preserve the equilibrium, or, in nautical phrase, 

 keep the fish on an "even keel." The ventrals are used 

 principally in rising, and the pectorals in backing, and keep- 

 ing the fish stationary ; when they are used alternately, and 

 not simultaneously, as any other pair of fins. 



The eye of the fish has no lids, as land animals have, but 

 a very thin transparent membrane drawn over it, which does 

 not give it the power of excluding the light ; hence the eyes 

 are always open, whether awake or asleep — if a fish can be 

 said to sleep. By the prominence of its eyes it is able to 

 direct its sight, somewhat backward and downward, as well 



