26 



BLIND VERTEBRATES AND THEIR EYES. 



THE CAVE RAT AND ITS EYES. 1 



The cave rat, Neotoma magister, ranges eastward to southern New York and 

 south to Alabama, and is not confined to caves. It lives in "cliffs, caves, and rock 

 ledges of the mountains, descending into the lowlands, where limestone caves afford 

 it security." 



In White's Cave, near Mammoth Cave, Kentucky, it has its nests near the 

 entrance, in the twilight region. In Mammoth Cave I found it in Mammoth Dome, 

 and it occurs also farther in, far removed from the twilight area. 



Rhoads (Jour. Cin. Soc. Nat. Hist., xix, No. 2, 55, 1897) says of it: 



Any suspicion of blindness or deficient eyesight, such as is exemplified in some of the lower 

 orders of animal life in the cave, can not attach to this mammal. As in all the more strictly noc- 

 turnal rodents, the eyes of this species are greatly developed; nevertheless, they are able to make 

 most intelligent use of them in broad daylight, if need be. 



In his "Origin of Species," sixth edition, vol. 1, page 171, Darwin says that 

 the eyes of Neotoma of Mammoth Cave are "lustrous and of large size; and these 



Fig. 1. (a) Eye of Mammoth Cave Rat. (b) Eye of Common Gray Rat. 



animals, as I am informed by Professor Silliman, after having been exposed for 

 about a month to a graduated light, acquired a dim perception of objects." The 

 cave rat, Neotoma, is still abundant in Mammoth Cave. Its tracks are numerous, 

 and in places little paths have been made by the rats where they run backward 

 and forward along ledges of rock. Since, however, a track once made in a cave 

 remains unchanged by wind or weather, the abundance of rats, as judged by their 

 tracks, may be misleading. A number of traps were set in the rotunda. During 

 three days one trap was sprung and one had the bait removed. No rats were 

 caught in the traps and none were caught alive. The author discovered one rat 

 rolling a mouse trap about which was too small for it to enter. When approached 

 with a light, the rat turned about and stared at the light. It then ran to a pile of 

 rocks, but did not attempt to hide ; instead, the rat ran to one end of the pile, then 

 along the top back to where it had stood, then stopped and again stared at the light. 



1 The histology of the eye is condensed from Dr. J. B. Slonaker's account, from which figures I and 2 are 

 taken. See Proc. Ind. Acad. Sci. for 1898, p. 255, 1899. 



