7(3 



They are usually arranged in two rows on each gill arch, with frequently 

 one also on the pharyngeal, behinrl the last gill slit. Occasionally only 

 one row is (hiveloix-d on each gill ih'kc ■•hcrring"j. and commonly the sec- 

 ond row. if ))resent, is less prominent than the first. The shovel fishes 

 are, however, an excei)tion 1o this latter statement, for in them tx)th rows 

 are equally and remarkably developed. As the anterior rakers guard the 

 relatively large passage-way bet\Veen thp foremost gill and the opercle, 

 while the other rows merely prevent the escape of objects between the 

 several i)airs of gills, the anterior row is almost invariably longer than 

 the remaining series. The shovel fish and the gi/zard shad are exceptions. 

 The rakers of this row are commonly longest in the middle of the arch. 

 shortening toward each end: but the ])art iculars of this disposition depend 

 on the length and shape of the arch and the concavity of the inner sur- 

 face of the opercle. In the gizzard shad, however, the short but very nu- 

 merous and fine gill-rakers project in a nearly horizontal direction. 



The gill-rakers, when short and ineffective, are often armed with min- 

 ute denticles, variously arranged, but are never branched or pinnate. In 

 several of the sucker family, the rakers of the lower horizontal arm of the 

 arch are represented by a thick, broad pad, transversely ridged (the ridges 

 representing the separate rakers) so that when approximated these struc- 

 tures form a continuous floor tor the sides of the buccal cavity. The rak- 

 ers 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 Hsh: and 

 in length from mere tubercles, to two or three times the length of the 

 corresponding filaments of the gill. Rarely they are completely wanting, 

 as in the pike. The anterior row is commonly so set iipon the arch as to 

 be obliquely divaricated by the separation of the branchial structures be- 

 ing thus automatically adapted to the respiratory movements. 



They are little developed in young fishes, the small liranchial arches and 

 the narrow slits between them serving to separate f"om the water the 

 minute objects of their earliest food. Their develo])ment with the growth 

 of the flsli simply enables it to retain as elements of its dietary, objects 

 which the coarseness of its branchial structures would otherwise compel 

 it to forego. 



Concerning their relation to food prehension, we nuiy 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 (ex- 

 cept for the smaller fishes) that the species is either piscivorous or feeds 

 largely upon niolUisks, the dental and jjliaryngcal a])paratus easily show- 

 ing which. 



The pike-perch (Stostedion) is somewliat remarkable in the fact that al- 

 though strictly piscivorous when adult, it has long and strong gill-rakers, 

 much longer in fact than in the less piscivorous related species, the com- 

 mon perch. In this case the rakers seem to have been retained, and even 

 further develoi)ed. as a liasis of attachment for several rather large recurved 

 teeth borne on theii- inner surfaces, useful in preventing the escai)e of a liv- 

 ing prey. 



The masticatory ajijiaratus of fishes (sometimes wanting) comprises 

 always a pair of phar\'ngeal bones— the lower pharyngeal jaws, a pair of 

 modified branchial arches. These are comnuuily ojiposed by superior 

 pharyngeals, wliicb most fi'iMpiently consist of osseous and cuticular thick- 

 enings of the upiH-r ends of the gill arches— sonuMimes of only (Uie or two, 

 as in the catfish family. sonu>tinu's of all, as in the suntislu^s. In the 

 cyprinoids, the ui)])er pliaryngeal is a (luadrate or triangular pail, rarely, if 

 ever, toothed, borne ui)on an obliiiiie, expanded process of the basioccipi- 

 tal. In the sucker family the sickle-shaped lower pharyngeals act against 

 a more or less indurated jialalal arch supported by the same cranial pro- 

 cess, the tlrnuiess and width of this hardened band varv with the devel- 

 opment of the lower arches of the ajjparatus. In nuist of the Acanthopteri 

 and in the cattish family the lower i)haryngeals have a fusiform outline, varying 



