506 Illinois State Lahoratnnj of Natural History, 



by a thick, broad pad, transversely ridged (the ridges represent- 

 ing the separate rakers) so that when approximated these 

 structures form a continuous floor for the sides of the buccal 

 cavity. The rakers may vary in number in different species 

 from ten or twelve in a series, as in some sunfishes, to more 

 than five hundred, as in the shovel fish; and in length from 

 mere tubercles, to two or three times the length of the cor- 

 responding filaments of the gill. Rarely they are completely 

 wanting, as in the pike. The anterior row is commonly so set 

 upon the arch as to be obliquely divaricated by the separation 

 of the branchial structures, being thus automatically adapted 

 to the. respiratory movements. 



They are little developed in young fishes, the small bran- 

 chial arches and the narrow slits between them serving to sep- 

 arate from the water the minute objects of the earliest food. 

 Their development with the growth of the fish simply enables 

 it to retain as elements of its dietary, objects which the coarse- 

 ness of its branchial structures would otherwise compel it to 

 forego. 



Concerning their relations to food prehension, we may say 

 in general that if numerous, long, and fine, they indicate the 

 importance of Entomostraca to the fish. If less numerous, 

 but moderately long and stout, in a fish of medium size, we 

 may presume that insects form a considerable ratio of the food. 

 If wanting, or rather short and strong, the presumption is 

 (except for the smaller fishes) that the species is either pisciv- 

 orous or feeds largely upon mollusks, the dental and pharyngeal 

 apparatus easily showing which. 



The pike-perch (Stizostedion ) is somewhat remarkable in 

 the fact that although strictly piscivorous when adult, it has 

 long and strong gill-rakers, much longer in fact than in the 

 less piscivorous related species, the common perch. In this 

 case the rakers seem to have been retained, and even further 

 developed, as a basis of attachment for several rather large 

 recurved teeth borne on their inner surfaces, useful in preventing 

 the escape of a living prey. 



The masticatory apparatus of fishes (sometimes wanting) 

 comprises always a pair of pharyngeal bones, — the lower pharyn- 

 geal jaws, a pair of modified branchial arches. These are 



