12 COPEIA 



bus seems to have continued until modern times in 

 various quarters of the globe; so at least the writer 

 is informed by Dr. E. W. Gudger, who has collected 

 a number of reports to that effect. 



Charles R. Eastman, 



New York, N. Y. 



CERTAIN FAMILIAR STRUCTURAL 

 ADAPTATIONS IN FISHES. 



That habit and structure are correlated will be 

 questioned by no student of evolution. That habit 

 determines structure would probably be less widely 

 conceded. If it does so, specialized structures would 

 be expected to arise among fishes already possessing 

 habits to take advantage of them ; we would expect 

 to find the habit served by a fish's peculiar structure, 

 shared also, to some degree, by its relatives which 

 lack the structure; and notable cases where this expec- 

 tation is realized are evidence that structure is deter- 

 mined by habit. 



Some such cases come to mind. The sailfish, 

 remarkable for its great expanse of dorsal fin, is said 

 to come to the surface of the sea with the fin out 

 of water, functioning as a sail in the wind. The 

 sword-fish and mackerel, its allies, are surface fishes, 

 the sword-fish at least often swims with its back-fin 

 out of water. 



The prehensile tail of the sea-horse with which 

 it coils around and holds fast to sea-weed is a struc- 

 ture unique among fishes. The pipe-fishes, its nearest 

 allies, live among sea-weed twisting their lithe bodies 

 among and bracing their tails against the strands of 

 weed. 



The highly developed breast-fins of the flying 

 fish which enable it to travel considerable distances 

 through the air and elude predaceous fishes of which 

 it is the prey, is one of the most remarkable structural 

 adaptations to be found in the world's ichthyfauna, 



