120 



BLIND VERTEBRATES AND THEIR EYES. 



Measurements of the Eyes of Chologaster in Groups. 



[Treated alike.] 



Measurements of the Retina of Species of Chologaster. 



It is seen that the retina of agassizii differs from that of papilliferus almost alto- 

 gether in the decrease of the thickness of the pigment epithelium. The retina of 

 cornutus differs from that of agassizii in the reduction of the layers inside of the 

 pigment epithelium. 



TYPHL1CHTHYS SUBTERRANEUS. 



The eye of Typhlichthys subterraneus has not heretofore been made the sub- 

 ject of study. The following account is based on 3 specimens, 20, 25, and 45 mm. 

 long respectively, from a small cave in the town of Glasgow, Kentucky, and a 

 number of specimens of various sizes, the largest 54 mm., from Mammoth Cave, 

 Kentucky. These were all collected by myself in the early part of September, 1897. 



The eye of this species is in general less degenerate than that of Amblyopsis. 

 The accessory structures are, on the other hand, much more degenerate than in 

 Amblyopsis. The eye can not be seen from the surface. The region of the eye 

 is, however, more conspicuously apparent than in Amblyopsis on account of the 

 thinner tissues of this smaller species through which the orbital fat-mass can be 

 seen. The 'eye can not be seen even in heads cleared with oil on account of 

 the almost total absence of pigment about the eye and its total absence in the 

 eye itself. 



