30 BLIND VERTEBRATES AND THEIR EYES. 



No definite information has been obtained as to their habits in nature. They 

 show no reaction to light, either as a response by motion to the direction of the 

 rays or to the quantity of light. If kept in a vessel, half of which is dark and the 

 other half light, the animal is found about as often in one as the other, and on 

 emerging into light from the dark it indicates in no way an awareness of the 

 difference. If in a tangle of plants, as watercress, they are found about the same 

 as in any other part of the vessel. 



If they are headed against a current, the flowing water acts as stimulus, urging 

 them on. If the current strikes them from behind, they move more rapidly in the 

 direction of flow. 



The sense of touch is highly developed. There is, however, no experimental 

 evidence that this is confined to any particular region. If the surface of the body 

 is touched anywhere except at the blunt truncated snout, the animal responds at 

 once by moving away. If the stimulus causes it to swim away, it may go (say 

 12 or 16 inches) till it strikes the side of the vessel, after which it soon comes to a 

 standstill. If, however, it is struck, say with the flat side of a scalpel handle, 

 sufficiently hard to move the entire animal even an inch backward, it may not 

 react, and this may often be repeated before it reacts by moving away. A possible 

 explanation of this fact is that in normal life it is every day striking itself against 

 obstacles, especially the sides of the vessel (when in confinement). 



The animal is exceedingly sensitive to any motion of the water. Where one is 

 kept in water about an inch deep, with its head near the surface, waves of water 

 set going by a gentle puff of the breath act as a sure stimulus. 



But little evidence thus far shows in favor of a sense of smell. All attempts 

 at feeding (except one) have been in vain. No attention was given to meat or 

 other articles placed near it. Examination of a dead specimen showed chitinous 

 remains of such Crustacea as Cyclops. 



If a glass rod or other object is held a little to one side and in front of the ani- 

 mal, it will cautiously turn its head in the direction of the rod. If the latter is then 

 made to describe an arc about the side of the salamander, the head will follow it 

 with a continuous motion, expressive of the greatest caution, as far as it can be 

 followed without moving any of the limbs. A sudden jar, produced by tapping 

 the rod on the bottom of the aquarium at such a time, causes the salamander to 

 jerk its head back and rear back on its limbs as far as it can. The same effect 

 is produced if the rod is introduced too rapidly. 



If a piece of crayfish tail is held by pincers in the fingers a short distance in 

 front or on one side of the head of the salamander, there is the same cautious motion 

 forward till the snout comes in contact with it. There is then a momentary hesi- 

 tation, followed by a sudden snap and seizure. 



The salamander may be pulled from side to side by the meat, after it has once 

 secured a hold, without causing it to let go. All of its caution is apparently directed 

 in approaching the food without disturbance. After it has secured a hold it will 

 struggle to maintain it. 



