THE STRUCTURE OF BLIND FISHES. 57 



to procure its food can never become a cave form. Sunfishes, 

 which are annually carried into caves, belong to this class of fishes. 

 They are always poor when found in the caves, and will never be 

 able to establish themselves in them. On the other hand, there 

 are no reasons why fishes detecting their prey either by smell or 

 touch should not be capable of colonizing caves. The catfishes and 

 Amblyopsida3 belong to the latter class. It is surprising that more 

 catfishes have not established themselves in caves. Among the 

 Amblyopsidse even those with functional eyes depend on touch 

 and vibrations for their food. Chologaster has well-developed tac- 

 tile organs and poor eyes. It is found chiefly at the mouths of 

 underground streams, but also in the underground streams them- 

 selves. The tactile organs are not different in kind from those of 

 other fishes, and their high deA^elopment is not more marked than 

 their development in the barbels of the catfishes. The charac- 

 ters which distinguish Chologaster as a fish capable of securing its 

 food in the dark are emphasized in Typhlichthys, and the tactile 

 organs are still more highly developed in Amblyopsis. The eyes 

 of the last two genera are so degenerate that it is needless in this 

 connection to speak of degrees of degeneration. On account of 

 the structure of their eyes and their loss of protective pigment they 

 are incapable of existence in open waters. With the partial and 

 total adaptation to an underground existence in the Amblyopsidse 

 and their negative reaction to light, it is scarcely possible that for 

 this family the idea of accidental colonization can be entertained 

 for a moment. Their structure is not as much due to their habi- 

 tat as their habitat is to their structure and habit. 



Typhlogobius lives in the holes of shrimps under rocks on the 

 coast of southern California. It is a living example of the ori- 

 gin of blind forms in dark places remote from caves. Here again 

 the " accidental " idea is preposterous, since no fish could by acci- 

 dent be carried into the devious windings of the burrows they 

 inhabit. Moreover, a number of related species of gobies occur 

 in the neighborhood. They live ordinarily in the open, but always 

 retreat into the burrows of crustaceans when disturbed. The ori- 

 gin of the blind species by the gradual change from an occasional 

 burrow seeker to a permanent dweller in the dark and the conse- 

 quent degeneration of the eye is evident here at once. Among 

 insects the same process and the same results are noted. We have 

 everywhere the connection of diurnal species with dark-loving and 

 blind forms, a transition the result of habit entered into with 

 intent, but no evidence of such a connection as the result of acci- 

 dent. Also numerous instances of daylight species being swept 

 into caves, but no instance of one establishing itself there. 



