166 THE STORY OF FISH LIFE. 



preys upon the larval eels, Leptocephali (p. 132), 

 which at certain seasons abound there. This 

 we know, because large numbers of these once 

 mysterious fish have been taken from the 

 stomachs of stranded sun-fish. When at the 

 surface the sun-fish swims by vibratile motions 

 of the curiously shortened tail-fin, which acts 

 precisely like the dorsal fin of the sea-horse 

 described above. On diving the dorsal-fin is 

 brought into requisition, and apparently by a 

 sort of sculling motion aff'ects the desired 

 descent, and perhaps the ascent. 



These two modifications are sufficient to call 

 attention to the importance of a careful study of 

 the external form as a whole, as well as of the 

 individual parts, of fishes. 



CHAPTER XIII. 



PEDIGREES. 



The pedigrees of most of us are like our worldly 

 possessions, small in compass. The proverbial 

 " mists of antiquity " — the limbo to which all 

 obscure things are assigned — begin with them at 

 about the third generation, if they carry us back 

 so far. Occasionally some one or other of us, 

 for various reasons, desires to know more of his 

 descent, and in such cases calls in the aid of the 

 trained specialist, who, like some other specialists, 

 fills in from his imagination the "missing links," 

 and in the end furnishes the desired and much 

 treasured "genealogical trees." 



