8 BLIND VERTEBRATES AND THEIR EYES. 



The Mitchell Caves can be traced for over 2 miles. Given that they are 3 

 kilometers long, their average width is perhaps 8.3 meters. This would give an area 

 of 25,000 square meters. Asa stream flows their entire length a direct comparison 

 can be made with epigean conditions by taking a stream of similar size and length 

 above ground, with territory equaling the width of the cave. The fauna of the 

 epigean area of equal size is incomparably richer than the subterranean one. 1 



The biological environment of cave animals is comparatively simple. While 

 much has been written on them, the only account of the interrelation of the animals 

 of any cave has recently appeared in a publication by one of my students, Mr. 

 A. M. Banta (publication No. 67 of the Carnegie Institution of Washington). 



1 For a discussion of the age of caves see page 1 7. 



