THE STRUCTURE OF BLIND FISHES. 



55 



and two explanations are prominent among those suggesting its 

 solution : 



1. The explanation of Lankester seems either a pleasantry or 

 the most unwarranted speculation. He says: "Supposing a num- 

 ber of some species of Arthropod or fish to be swept into a cavern 

 or to be carried from less to greater depths in the sea, those indi- 

 viduals with perfect eyes would follow the glimmer of light, and 

 eventually escape to the outer air or the shallower depths, leaving 

 behind those with imperfect eyes to breed in the dark place. A 

 natural selection would thus be effected. In every succeeding gen- 

 eration this would be the case, and even those with weak but still 

 seeing eyes would in the course of time escape, until only a pure 

 race of eyeless or blind animals would be left in the cavern or 

 deep sea." 



This process does not, of course, account for the degeneration 

 of the eye beyond blindness. But, aside from this objection, the 

 humor of his " glimmer of light " impresses itself very forcibly 

 on one after spending a day in following the devious windings of a 

 living cave, not to mention his tendency in cave animals, which 

 are negatively heliatropic, to follow it. There are other objec- 



Fig. 7.— Later 



Amblyopsis, showing the location of the tactile ridges. 



tions. Fishes arc annually swept into the caves, but they are not 

 able to establish themselves in them. To do this they must have 

 peculiar habits, special methods of feeding and mating before a 

 successful colonization of caverns can become successful. Fur- 

 ther, if the origin of the cave fauna is due to accident, the acci- 

 dent must have happened to four species out of six of the Amblv- 



