504 Illinois State Lahondonj of Xatural Hisfori/. 



strain from the waters, or to separate from the nmd, but that 

 psychological preferences as well as physical capabilities have 

 something to do with their choice of food. 



THE STRUCTURES OF ALIMENTATION. 



A brief review of the principal facts respecting the struct- 

 ures of alimentation in fishes will be necessary to exhibit 

 clearly the relation of habit and organization in this particular. 



These structures may be conveniently divided into those 

 of search^ of prehension^ of mastication, and of digestion. 

 Means of defence and escape may also properly be mentioned, 

 as belonging to the obverse side of the food relation. 



Structural peculiarities relating to the methods and situa- 

 tion of the search for food are illustrated by the barbels of the 

 catfishes and the sturgeons, the shovel of Polyodon, the square 

 head of the stone roller, the flat heads of the top minnows, and 

 the pointed snouts of the darters, — which fit them for prying 

 about between and under stones in running water. Similarly 

 related, are the bare breasts of many darters and the large 

 pectoral fins of the stone roller and Phenacobius. 



The structures of food prehension are the lips, the jaws, 

 the teeth, and the gill-rakers, with which should be considered, 

 perhaps, the gill slit or branchial opening. The sucking lips 

 of the Catostomatidse, organs of touch as well as of prehension, 

 are of course related to the mud-searching habit of these fishes, 

 the protractile jaws aiding in this use. The stout wide jaws of the 

 catfishes, with their wide bands of minute, pointed teeth, are 

 probably to be understood as an apparatus for seizing, holding, 

 and pulling about relatively large objects, whether hard or soft, 

 and are perhaps most useful in feeding upon mollusks. The 

 very large but weak jaw of the shovel fish is explained by the 

 minute character of its food, which offers no resistance, but 

 necessitates the passage of large quantities of water through 

 the mouth; while the long and slender jaws of the long-nosed 

 gar (Lepidosteus) armed with several rows of acute raptatorial 

 teeth, are the best apparatus in our waters for the destruction 

 of a relatively small but active living prey. 



