MUSICAL FISH. 439 
The so-called ‘* mucous canal” or lateral line of fishes and 
Amphibians is sensory. It consists of small masses of 
nerve-epithelium, arranged in linear series along the sides of 
the head and body, having hair-cells continuous with nerves. 
They are called ‘‘nerve-buttons” or ‘‘ nerve-heaps.” Accord- 
ing to Schultze, their office appears to be to appreciate mass- 
movements of the water, and more particularly vibrations, 
which have longer periods than those appreciated by the ear 
(Dercum). In the blind-fish of the Mammoth Cave a row 
of sense-papille is situated on the front of the head, sup- 
plied with nerve-fibres sent from the fifth pair of nerves 
(Wyman). 
The angler (Lophius piscatorius) has long been known to 
possess hinged teeth, capable of being bent inward toward 
the mouth, but by virtue of the elasticity of the hinge at 
once resuming the upright position when pressure is removed 
from them. <Anadbleps and Pecilia have also movable teeth. 
The hake, a voracious predatory fish, and in a less degree 
other Gadide, are possessed of hinged teeth. 
The nature of respiration is intimately connected with the 
production of sounds by fishes. Recent researches by Jobert. 
on certain unusual modes of breathing in fishes are of speciak 
interest. He has examined certain fishes of the Amazons, 
t.¢., species of Callichthys, Doras, Erithrinus, Hypostomus. 
and Sudis gigas or ‘‘ pirarucu” of the natives, the latter being 
allied to the herring. In the Caillichthys the intestine is trans- 
formed into a respiratory organ. When the water dries up 
it emigrates.to other pools or streams, creeping by means. 
of its pectoral fins. This fish can live twenty-four hours: 
out of the water with impunity. 
In the gigantic pirarucu, the swimming-bladder is a long 
sac, and the upper part does not look like that organ, being 
spongy, areolar, reddish-brown, friable, and intimately 
pressed to the dorsal and lateral walls of the body ; its color 
recalls that of the lungs of a bird, and functionally it re- 
sembles the latter. 
Among accessory breathing organs are the lamellate cavity 
of the Anabdas, and the sac-like appendages which are in con- 
nection with the gill-cavity, and extend under the muscles 
