No. i.] BLIND VERTEBRATES OF NORTH AMERICA. 35 



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 bead-like 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 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 opening 

 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. Fig. i, a, is a 

 median section of the lids and corneal epithelium of an eye 

 .954 mm. in diameter, taken from an adult specimen 106 mm. 

 in length. In this section the upper lid overlaps the lower 

 lid .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 entire 

 eye. The orbital slit is .17 mm. in length. The conjunctival 

 pocket extends some distance forward and backward 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 animal. (See comparative measure- 

 ments of the eyes at the close of the paper.) 



The following is a series of measurements on the larvae of 

 Typhlotriton. 



ROCK HOUSE CAVE. ROCK HOUSE CAVE. MARBLE CAVE. 



Specimen ... 54 mm. long. 78 mm. long. 88 mm. long. 



Size of pupil . . .432 mm. .640 mm. 



Length of eye . . 1.30 mm. 1.50 mm. 1.60 mm. 



From optic nerve 



to front of lens . .80 mm. 1.20 mm. 



Vertical diameter 1.248 mm. 1.28 mm. 



Sections of the adult and larva from Marble Cave were made 

 in the usual manner. The six normal eye muscles were pres- 



