Slonaker, Eye of the Mole. 361 



of the lens, the lack of a vitreous chamber, the closed lids and 

 the condensed condition of many of the retinal elements all 

 signify that, at best, the adult mole can do no more than distin- 

 guish between light and darkness. 



A few experiments on the living animal seem to substan- 

 tiate this assertion. An adult was placed on a table in the 

 direct sunlight. It always started in a forward direction re- 

 gardless of its orientation with reference to the sun. It would 

 maintain this direction until it came in contact with some obsta- 

 cle. It would as often go directly toward the sun as away from 

 it. Light therefore had very little effect as the stimulus was 

 insufficient to cause a change in the direction of locomotion. 

 Shearing the fur from in front of the eye did not modify the re- 

 sults. The mole is decidedly stereotropic and is not quiet so 

 long as it is not under something. I found that it would just 

 as readily crawl and remain under a pane of clean glass in bright 

 sunlight as under a board in the shadow. My experiments 

 lead me to conclude, therefore, that the eye of the common 

 mole is quite incapable of being stimulated to such a degree as 

 to cause any modification in the activities of the animal. 



Summary. 



The eye of the common mole appears as an inconspicuous 

 dark area situated well forward on the side of the snout. It lies 

 imbedded in the muscle beneath the skin. 



When the eye of the common American mole is compared 

 with that of the European mole it is found to be much more de- 

 generate in all its parts than the latter. 



The eye is degenerate and is no longer capable of function- 

 ing in distinct vision. The most noticeable changes which have 

 occurred as contrasted with a normal mammalian eye are: — 



1. The fusion of the lids, thus reducing the eye cleft to a 

 microscopic tube which is probably incapable of functioning in 

 a normal manner. 



2. The great reduction in the relative size of the eye. 



3. The much crowded condition of the retina as a result 

 of the decrease in the size of the eye as a whole. 



