EYES OF THE TEXAN CAVE SALAMANDER. 



31 



THE EYES OF TYPHLOMOLGE RATHBUNI. 1 



The U. S. Fish Commission, through Dr. B. W. Evermann, sent me four speci- 

 mens of this salamander and a number of its eggs. Of these, one adult had been 

 received in Washington, April 8, 1896, and three young, of different sizes, March 

 1, 1896. A few eggs were laid about March 15, 1896. The late Professor Nor- 

 man, of the University of Texas, and Professor Bray, of the same place, secured me 

 an additional number. Later, I visited the caves and the artesian well at San 

 Marcos, and have been able to observe the living specimens. The specimens 

 sent by Professor Evermann were preserved in alcohol; those sent by Professor 

 Norman had been killed in Perenyi's fluid. The sections were stained chiefly in 

 Biondi-Ehrlich's tricolor mixture. 



The following gives the dimension of the eyes in a number of individuals. 

 Professor Norman sent only the heads, so the length of his specimens sent can 

 be given only approximately. The sizes (in millimeters) were obtained by compar- 

 ing the distance between the eyes, with the same distance in entire specimens. 



Dimensions of the Eyes of Typhlomolge in Millimeters. 



The eye of Typhlomolge is, in many respects, much more degenerate than that 

 of its European caverniculous relative, Proteus. In Proteus the six muscles are 

 all present; in Typhlomolge they have entirely disappeared. In the former all the 

 layers normal to the retina are present; in the latter the conditions are much 

 simpler. In Proteus the lens is still present and blood-vessels still enter the eye; 

 in Typhlomolge no trace of the lens could be found, except in one individual, and 

 blood-vessels no longer enter the eye. While some of the asymmetry may have 

 been caused by reagents, it is evident that there is a great deal of fluctuation in 

 the shape of the eye. The eye is irregular-oval in outline as seen from above, but 

 the optic nerve enters it at the posterior half of its inner face. The eye increases 

 materially in size from the smallest to the largest of specimens examined. This 

 increase is not directly proportional to the increase in the length of the animal, 

 so the young have relatively larger eyes (fig. 4). 



The eye lies immediately beneath the skin, to which it is attached by a connective 

 tissue mass which is horizontally elongate. The axis of the eye makes an acute 

 angle with the surface of the skin, the eye being directed outward and forward. 

 The dermis over the eye does not differ from that in the neighboring tissues. The 

 epidermis, in the largest individual, is perceptibly thinner over the eye, i.e. from 

 the continuation of the axis of the eye to the surface of the epidermis. The measure- 

 ment, in the largest individual, of the epidermis at a point over the eye and 320 /u 

 above and below this point gives the following: thickness over the eye 73 fi, 

 320 [j. above the middle of the eye 96 /a, 320 /a down from the eye 80 /x. 



1 See Trans. Am. Microsc. Soc. xxi. p. 49, 1900. 



