COMPARATIVE STUDY OF SCOMBROID FISHES. 
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the lighter, visceral part. The posterior end of the body is more slender than 
the anterior, the broadest part of the body being generally in advance of the 
middle, between the snout and the caudal peduncle. In mackerels the broadest 
portion is found in the vertical, passing the middle of the first dorsal, that is 
a little before the middle of the body. In seerfishes the broadest part lies at 
the posterior pari of the first dorsal or near the anus. In tunnies the broadest 
pari of the body is at the middle of the first dorsal, while in bonitos the broadest 
pari nearly coincides with the middle of the body. The body is generally rounded 
or elliptical in cross-section. In Bastrelliger and most species of the genus 
Cybium the body is more or less compressed ; but in the Flecostei the body is 
always plump. 
Generally the line connecting the apex of the snout and the middle of the 
side of the tail passes through the centre of the eye, and nearly coincides with 
the upper margin of the pectoral fin. In the Scombridæ the nape is narrow, 
and the body is more or less compressed laterally ; in the Cybiidæ the nape 
is broad, and the body is generally compressed and elongated ; while in the 
Placostei the body is short and plump. In the Thunnidae the nape is broad, but 
in the Katsuwonidæ it is remarkably narrow. The caudal portion is shorter than 
the abdominal portion in the Scombridæ ; longer in the Cybiidæ, except in the 
genera Acunthocybiurn, Sarda, and Gymnosarda ; nearly equal in the Thunnidæ ; 
and shorter in the Katsuwonidæ. In the Scombridæ the caudal peduncle is 
thick, nearly rounded in cross-section and wants the lateral keel, while in the 
Cybiidæ it is rather thick, more or less horizontally depressed, and is provided 
with a large lateral keel, which is rather thin and broad at the hind end. In 
the Plecostei the caudal peduncle is very narrow, depressed, and is provided with 
a very thick keel, especially in the Katsuwonidæ. In the Cybiidæ these keels 
are generally covered were elongated scales, but they are quite naked in the 
Plecostei. 
The form of the body differs of course in different ages of fish. Generally 
the head is longer in small, immature specimens, but the proportion of its 
length to the height of the body is often constant. Therefore immature 
specimens of seerfishes and their allied forms, such as Cybium niphonium, C. 
cornmerson, and Sarda orientcdis are broader than the mature forms ; but in the 
Plecostei the immature forms have a more slender body than the adult. The 
