﻿20 BLIND VERTEBRATES AND THEIR EYES. 



to scleral cartilages, and if it did they would not develop several sizes too large 

 for the eye. At present no known epigcan species of the Amblyopsidse possesses 

 scleral cartilages. The ancestry of rosa is hence unknown. Amhlyopsis has the 

 scleral cartilages, and the eye of ros(B passed through a condition similar to that 

 possessed by Amhlyopsis, but the latter species has ventral fins and is hence ruled 

 out as a possible ancestor of roscc. The epigcan ancestry of Amhlyopsis is also 

 unknown. The ancestry of Typhlichthys being quite distinct from that of rosce, 

 the latter species is referred to a separate genus, Troglichthys. 



Judging from the degree of degeneration of tlic eye, Troglichthys has lived in 

 caves and has done without the use of its eyes longer than any other known 

 vertebrate. (Ipnops, being a deep-sea form, is not considered.) 



The species of Typhlichthys differ from each other in only a few inconspicuous 

 respects. (See page 53.) 



