VIVIPAROUS FISH. 441 



produces " a gentle humming sound ;" eels utter a more dis- 

 tinctly musical sound than any other of those observed by 

 Abbot, who states that "it is a single note, frequently re- 

 peated, and has a slightly metallic resonance.'' It should 

 also be noticed that the organs of hearing in many musical 

 fishes are said to be unusually well developed, hence these 

 sounds are probably love-notes ; and Abbot notices the fact 

 that these fishes are dull-colored during the reproductive sea- 

 son, as well as at other times, while voiceless fishes, such as 

 the perch, common sun-fish, chub, roach, etc., are highly 

 colored during the breeding season, and thus the sexes are 

 mutually attracted in the one case by music, and in the other 

 by bright colors. Finally the sounds of fishes may be said 

 to be homologous with those of reptiles, birds and mammals, 

 the air-bladder being homologous with the lungs of the 

 higher Vertebrates, while the pneumatic duct is comparable 

 with the trachea of birds and mammals. 



In swimming, the propelling motion is mainly exerted by 

 the tail, the movements of which are somewhat like those of 

 an oar in sculling. The spines of the tail-fin are movable, 

 and are capable of being brought into such a position that 

 the tin will meet with less resistance from the water while the 

 tail is bent, they are then straightened, and it is when being 

 straightened that the fish is propelled. The movements of 

 the pectorals and ventrals are to steady the fish and to ele- 

 vate and depress it, while the dorsal and anal fins steady 

 the body and keep it upright, like a dorsal and ventral keel. 



Among viviparous bony fishes are certain Cyprinodonts 

 (as Anableps and Pcecilia), the eel-like Zoarces, and the 

 blind-fish of the Mammoth Cave. A small family of Cali- 

 fornian marine fishes, in form resembling the sun-fish (Pomo- 

 tis) are called by Agassiz Embiotocidce, from the fact that 

 they bring forth their young alive. Emblotoca JacTcsonl 

 Agassiz, which is twenty-seven and a half centimetres (10^ 

 inches) long, has been known to produce nineteen young, 

 each about seven and a half centimetres (3 inches) long. 



During their reproductive season, many bony fishes, such 

 as the stickleback, salmon, and pike, are more highly colored 

 than at other times, the males being especially brilliant in 



