400 FISHES 



the north of that river Amblyopsis occurs alone. The sense 

 whose delicacy compensates for the absence of eyes in the blind 

 fishes seems to be the sense of touch, or rather we should say 

 the sensitiveness of the skin to vibrations. As in the Cyprino- 

 dontidae, no lateral line is externally visible in the Amblyopsidaa, 

 but whether the tube with its sense-organs is entirely absent is 

 not stated. The surface of the skin is covered with sensory 

 papillae which are possibly of the same kind as the sense-organs 

 of the lateral line and serve instead of the latter. Professor Cope, 

 from observations on Amblyopsis in its natural habitat, stated 

 that if not alarmed they come to the surface to feed and look 

 like white aquatic ghosts, that they could then be easily taken 

 by the hand or by net, provided no noise was made, for 

 their sense of hearing was very acute, and at the slightest sound 

 they swam down and hid beneath stones at the bottom. Miss 

 Hoppin, on the other hand, found from observations on TypJi- 

 lichthys in captivity that it was insensible to noises made in the 

 air but immediately darted away if the side of the vessel was 

 struck or if the water was disturbed or if the fish itself was 

 touched. This seems to show that the fish was specially sensi- 

 tive to the stimuli which Parker found to be perceived by the 

 lateral line organs in Fundulus. 



With regard to the evolution of the blind cave-fishes, the de- 

 velopment of the blindness in the individual must be admitted 

 to have an important bearing on the question of its origin in 

 the species. The Amblyopsidae, like the Cyprinodontidae, are 

 viviparous, and the development of the eyes in the embryo has 

 been carefully investigated by Eigenmann. The young are 

 born at a length of about half an inch, or 12 to 13 mm. The 

 eye develops as an outgrowth from the brain at the same stage 

 of growth as in normal fishes, when the embryo 'is 1*5 mm. 

 long, but grows little after its appearance. The lens develops 

 when the fish is T 5 mm. long, but never loses its embryonic 

 character, it soon degenerates and disappears altogether when 

 the fish is 10 mm. in length, that is before birth. The retina 

 and other parts of the eye have entirely degenerated by the 

 time the fish is 13 cm. or about 4 in. and its highest stage is 

 reached when the fish is 10 mm. long. This history of the 

 eye is, at least in the opinion of the present writer, more in har- 

 mony with the view that the blindness is due to the gradual 



