COMPARATIVE STUDY OF SCOMBROID FISHES. 
357 
relation with the nature of food. The gill-rakers are strainers, and chiefly serve 
to prevent the escape of food from the branchial cleft, thus they are best developed 
in the plankton-feeders, such as mackerels and bonitos ; but they are poorly de¬ 
veloped in voracious forms, such as seerfislies, and are entirely wanting in 
Acanthocybimn. At the same time the gill-rakers may serve “ to prevent any 
solid particles from passing into the gill-clefts and clogging or otherwise injuring 
the branchial filaments.” Gill-rakers are best developed on the external side of 
the first brancliial arch. They are long and bar the space between the opercle 
and the branchial arch. Other series of gill-rakers are developed on the inter¬ 
nal side and bar 1 the intervals between branchial arches or the interval lie tween 
the branchial arch and the lower pharyngeals. Gill-rakers on the external side 
of the brancliial arch are directed forward, while those on the internal side are 
directed backward. Gill-rakers he close to the brancliial arch -when the mouth 
is closed ; but are separated and make angles with the brancliial arch, when 
the mouth is open. The inner or upper side of the gill-rakers is rough, armed 
with minute tootli-like prickles. 
Li the Katsuwonidae the gill-rakers on the internal side of the branchial 
arches are well developed. The good development of gill-rakers on the upper 
arm of the first and second branchial arches is remarkable. 
In the Scombridae the gill-rakers are weak, longer than the gill-lamellae, 
and very numerous and closely set. Each gill-raker has two rows of alternating 
diverging flexible filaments, giving a villous appearance to the mouth-cavity. 
In this family the gill-rakers on the inner side of each branchial arch are pretty 
well developed. In Rastrelliger the gill-rakers are enormously long, so that they 
may be seen from the gape of the mouth. In the Cybiidae the gill-rakers are 
shorter than the gill-lamellae, rod-like, and few in number. Fine but stout tootli- 
like processes on the inner side of the gill-rakers are in two or more rows. In 
most species of this family external gill-rakers only are developed. In Sarda 
chilensis, however, I found a few, small internal gill-rakers on the first gill-arch. 
In the Plecostei the gill-rakers are thin, narrow lamellae with villous teeth 
on the inner side. As the gill-rakers are long, and the gape of the mouth wide, 
the former may easily be seen in the latter. In the species in which the num¬ 
ber of gill-rakers is large, they are well developed in other respects as well, so 
that among the Japanese tunnies, Thunnus Orientalin has the best developed gill- 
