COMPARATIVE STUDY OF SCOMBKOID FKHES. 297 



tlie lighter, visceral paa-t. The ixjsterior end of the body is more slender than 

 the anterior, the broadest pirt of the Ixxly being generally in advance of the 

 middle, liotween the snout and the cancLil ixxliincle. In mackerels the broadest 

 portion is finiiul iu the vertical, passing tlio middle of the first dorsal, that is 

 n little before the middle of the Ixxly. In setn'fishes the broadest part lies at 

 the pisttTior part of the first dorsiJ or ncai" the amis. In tnnnie3 the l)roadest 

 liart of the lK)dy is at the middle of the fii-st dorsal, while in bonitos the broiidest 

 pirt ncai-ly coincides with the middle of the body. Tlie body is generally roimded 

 or eUiptical in cross-section. In RastreUiger and most species of the genus 

 Cyhinm the body is more or less comprcastKl ; but in tlic Plecostei the body is 

 idways plnmp. 



Generally the line connecting the apex of the snout and the middle of the 

 side of the tail passes tlu'ough the centi'e of the eye, and nearly comcides with 

 the npp^r margin of the pectoral fin. In the Scombridfe the nape is iian-ow, 

 and the body is more or less compressed laterally ; in the Cybiidre the nape 

 is broad, and the body is generally compressed and elongated; "while in the 

 Placostei the body is short and plnmp. In the Thimnidae the nape is broad, but 

 in the Katsuwonidfo it is remai-kably uaiTow. The caudal portion is shorter than 

 the abdominal portion in the Scombridse ; longer in the Cybiida?, except in the 

 genera Acarähocj/hium, Sarda, and Gymnosarda ; nearly equal in the Thunnidae ; 

 and shorter in the Katsuwonidse. In the Scombridae the caudal peduncle is 

 thick, neai'ly rounded iu cross-section and wants the Literal keel, while in the 

 CybiidiC it is rather thick, more or loss horizontally depressetl, and is provided 

 with a large lateral keel, which is rather thin and broad at the liiud end. Li 

 the Plecostei the caudal peduncle is very nan-ow, depressed, and is pro\^ded with 

 a very thick keel, especially in the Katsuwouidro. In the Cybiidae these keels 

 ai-e generally covei^ed were elongated scales, but they we quite naked in the 

 Plecostei. 



The form of the body diflei-s of com-se in different ages of fish. Grenerally 

 the head is longer in snudl, immature specimens, but the proportion of ite 

 length to the height of the lwd\' is often constant. Therefore immature 

 specimens of seerfishes and their aUied forms, such as Cyhium niphonium, C. 

 commerscm, and Sarda orientalis are broader than the mature forms ; but in the 

 Plecostei the immatm'e forms have a more slender body tlian the adult. The 



