The Grayling and the Smelt 131 
oceanic depths. The “Bombay duck” of the fishermen of 
India is a species of Harpodon, H. nehereus, with large mouth 
and arrow-shaped teeth. The dried fish is used as a relish. 
The Benthosauride are deep-sea fishes of similar type, but 
with distinct maxillaries. The Bathypteroide, of the deep seas, 
resemble Aulopus, but have the upper and lower pectoral rays 
filiform, developed as organs of touch in the depths in which 
the small eyes become practically useless. 
Ipnopide.—In the Ipnopide the head is depressed above 
and the two eyes are flattened and widened so as to occupy 
most of its upper surface. These structures were at first sup- 
posed to be luminous organs, but Professor Moseley has shown 
them to be eyes. “They show a flattened cornea extending 
along the median line of the snout, with a large retina com- 
posed of peculiar rods which form a complicated apparatus 
Fig. 90.—Ipnops murrayi Ginther. 
destined undoubtedly to produce an image and to receive 
especial luminous rays.’”’ The single species, [pnops murrayt, 
is black in color and found at the depth of 24 miles in various 
seas. 
The existence of well-developed eyes among fishes des- 
tined to live in the dark abysses of the ocean seems at first con- 
tradictory, but we must remember that these singular forms 
are descendants of immigrants from the shore and from the 
surface. “In some cases the eyes have not been specially 
modified, but in others there have been modifications of a lumi- 
nous mucous membrane leading on the one hand to phosphor- 
escent organs more or less specialized, or on the other to such 
remarkable structures as the eyes of Ipnops, intermediate 
between true eyes and phosphorescent plates. In fishes which 
cannot see, and which retain for their guidance only the general 
sensibility of the integuments and the lateral line, these parts 
soon acquire a very great delicacy. The same is the case with 
