128 



BLIND VERTEBRATES AND THETR EYES. 



uniform in shape in different individuals or even the two sides of the same indi- 

 vidual. It can be located and seen in cleared heads solely on account of the pig- 

 ment which is always abundant over the distal face of the eye. It is located so far 

 beneath the surface as to occasionally lie in contact with the brain case nearly 

 opposite the posterior end of the olfactory lobe. It has thus been withdrawn 

 much farther than in the other blind species. 



It is very much smaller than the eye of either T. subterraneus or Amblyopsis. 

 Its size is, however, quite variable, measuring 40, 49, 56, 64, 54 by 96, 56 by 120 /x 

 in different instances, exclusive of choroid and sclera. 



brain 



Fig. 44. (a) Cross-section of Part 'of Head of Troglichthys, 25 mm. long, showing Position and 

 Proportions of Eye. 

 (l>) Head of Troglichthys from above, showing Relative Positions of Tactile Organs and Eyes, 

 (c) Part of Same Head, showing Eyes with their Peculiar Pigmentation and Distribution 

 of Pigment Cells in Surrounding Tissues. 



The muscles of the eye were in no case normal. I have not found more than 

 two rectus or more than one oblique muscle belonging to any one eye. They can 

 best be made out from horizontal sections. In cross-sections it is very difficult to 

 identify or follow them. 



The best-developed rectus was found in a specimen 35 mm. long. It is com- 

 posed of a number of normal fibers forming a bundle 20 y. in thickness, and from 

 its origin to its insertion it is 256 /a long. The remarkable peculiarity of this muscle 

 is that 100 /a of this is a tendon 4 juin thickness (fig. 46 b,msc.r.). The tendon spreads 

 into a cone-shaped mass of fibers attached to the proximal face of the eye. Traces 

 of two muscles were made out connected with the right eye of another individual. 



