EYES OF TYPHLOTRITON FROM MISSOURI. 



37 



In the larva- up to go mm. long the skin passes over the eye without forming a 

 free orbital rim and the eye does not protrude beyond the general contour of the 

 head. In the adult from 97 mm. on, the eye forms a beadlike projection. There 

 are in the adult distinct lids. These are closed over the eye, covering it entirely, 

 the slit being much too small for the eye. The lower lid is free from pigment, but 



FIG. 9. (a) Diagrammatic Representation of Eye of Typhlotriton drawn to scale. 

 (/>) Vertical Section through Cornea and Lids of Adult. 



the upper lid, which closes over the lower, is as thickly pigmented as any other 

 part of the body. 



Stejneger says of the eyes that they are "small, only slightly raised, and covered 

 by the continuous skin of the head, with only a shallow groove to indicate the open- 

 ing between the lids, the underlying eyes visible as two ill-defined dusky spots." 



In sections the lids are seen to overlap one another some distance, forming an 

 obscure, free orbital rim. Figure 9 b is a median section of the lids and cornea! 

 epithelium of an eye 0.954 mm. in diameter, taken from an adult specimen 106 mm. 

 in length. In this section the upper lid overlaps the lower lid 0.216 mm., or more 

 than one-fifth the diameter of the eye. Passing from the median section toward 

 the corners of the eye, the lower lid unites with the underlying tissue first. When 

 observed from the top, the upper lid covers the eye entirely. The orbital slit is 0.17 

 mm. in length. The conjunctival pocket extends some distance forward and back- 

 ward beyond the slit. The eye increases in size but little from the larval to the 

 adult stage and its growth is not proportional to the growth in length of the ani- 

 mal. (See comparative measurements of the eyes at the close of the chapter.) 



The following is a series of measurements (in millimeters) on the larvae of 

 Typhlotriton : 



Sections of the adult and larva from Marble Cave were made in the usual 

 manner. The six normal eye muscles are present in Typhlotriton. The m. 

 recti form a sheath about the optic nerve in its distal part and spread out from it 



