THE EYES OF AMBLYOPSIS. 



135 



Wyman was mistaken in his identification of Nos. 2 and 4, and part of 3. 



Of this species I have had an unlimited supply of fresh material from the 

 Shawnee Caves in Lawrence County, Indiana. I shall first give the histology of 

 the eyes of fishes from 25 mm. long to their maximum size, 135 mm. The details of 

 the development of the eye will follow. 



In well-fed adult specimens of Ambiyopsis there is no external indication of 

 an eye. In poor individuals the large amount of fat surrounding the eye and 

 collected in a ball-shaped mass becomes apparent through the translucent skin. 

 In young specimens, before they have reached a length of 50 mm., the eyes are 

 perfectly evident from the surface. By this I do not mean that they are conspicuous, 

 for the minute eyes would not be conspicuous were they situated just beneath the 

 skin. The skin is not modified in the region over the eyes, but has the same structure 

 it possesses in the neighboring regions. This condition is in strong contrast to 

 the conditions described for Chologaster papillifcrus. The position of the eye can 

 be determined from the surface in older individuals by certain tactile ridges, being 



I.e. 



It 



FIG. 4Q. (a) Section of Right Half of Head of Clwlogaster, through Eye. 

 (b) Section of Right Half of Head of Ambiyopsis, through Eye. 



between a long longitudinal ridge (supraorbital) situated caudad of the posterior 

 nares and two vertical (suborbital) ridges. They can also be approximately located 

 by the mucous canals, being situated above the middle of the suborbital canal 

 forward from the fork of the suborbital and rostral canals. The exact location in 

 relation to these ridges differs, however, to some extent in different specimens. 



The skull is surprisingly little modified, there being deep orbital notches, large 

 enough to accommodate a large eye. The maintenance of this skull structure 

 long after the eye has dwindled is significant in the consideration of the causes of 

 degeneration and will be referred to again. 



The change in the relation of the eye to surrounding tissues as well as the relative 

 size can best be gathered from the accompanying figures or cross-sections of Cholo- 

 gaster and of Ambiyopsis, drawn with the same magnification, but from different 

 sized individuals (figs. 49 a, b). 



Beneath the dermis (black in the figures) a thick layer of connective tissue has 

 developed in Ambiyopsis, The large fibrous capsule occupied by the eye, eye 



