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 reprodnctive 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 lke 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 fin 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 Pecilia), 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 Hmbiotocide, from the fact that 
they bring forth their young alive. ZHmbiotoca Jacksoni 
Agassiz, which is twenty-seven and a half centimetres (103 
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 
