COMPARATIVE STUDY OF SCOMBROID FISHES. 357 



ixilatiou with the nature of food. Tlie gill-rakors ai'e sti'ainei's, aud cliiefly sen-e 

 to iffovent tbc escape of food fnom the bmucbial cleft, thus they are best devulo^jed 

 in the pIiuikton-feed«irs, such as nmckei-ols and bonitos ; but the}' ai'o jxiorly de- 

 veloped in voracious fonns, such iV5 socrfishes, aud are eutirclj wjuiting iu 

 Acardhocybium. At the same time the gill-nikors nmy serve " to prevent any 

 solid particles fi'om passing into the gill-clefts aud clogging or otherwise injuring 

 ihe branchitil filamcuts." Gill-rakora are best developed on the external side of 

 the fii'st braucliial arch. They are long and bar the space between the o^xsrcle 

 and the branchial arch. Other scries of gill-rakers ai-e developed on the inter- 

 nal side and bar the intervals between branchial ai'ches or the interval l^etween 

 the branchial arch and the lower pharyngeals. GiU-rakers on the external side 

 of the braucliial arch are directed forward, while those on the intenml side are 

 directed backward. Gill-rakers He close to the branchial ai'ch when the mouth 

 is closed ; but are separated and make angles with the branchial arch, when 

 the mouth is open. The inner or upper side of the gill-rakers is rough, aimed 

 with minute tooth-Hke prickles. 



In the Katsuwonidae the gill-mkers on the internal side of the branchial 

 arches are well developed. The good development of gill-rakei-s on the upper 

 arm of the first and second branchial arches is remarkable. 



In the Scombiidae the gill-rakers are weak, longer than the gill-lamellae, 

 and veiy numerous and closely set. Each gill-raker has two rows of alternating 

 divei'giug flexible filaments, giving a villous appearance to the mouth-cavity. 

 In this fiuuily the gül-rakei-s on the inner side of each branchial arch are pretty 

 well developed. In RastreUiger the giü-rakei-s are enormously long, so that they 

 may be seen from the gape of the mouth. In the Cybiidae the gill-rakers ai'e 

 shorter than the gill-lameUae, rod-Hkc, and few in numbei'. Fine but stout tooth- 

 hke processes on the inner side of the gill-rakers are in two or more rows. In 

 most species of this family external gill-rakei3 only are developed. In Sarda 

 chilenm, however, I foimd a few, small internal gill-rakers on the fii-st gill-ai"ch. 



In the Plecostei the gill-rakers are thin, nan-ow lamellae with villous teeth 

 on tlie iimer side. As the gill-rakers ai'e long, and the gape of the mouth wide, 

 tlie former may easily be seen in the latter*. In the species iu which the num- 

 ber of giU-rakei"s is lai^e, they aie well developed in other respects as well, so 

 that amoug the Japanese tunnies, Thunniis wi&ü<dis has the best developed gill- 



