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 epigean species of the Amblyopsida? possesses 

 scleral cartilages. The ancestry of roses is hence unknown. Amblyopsis has the 

 scleral cartilages, and the eye of rosoe passed through a condition similar to that 

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

 out as a possible ancestor of rosce. The epigean ancestry of Amblyopsis 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 the 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.) 



