EYES OF THE TEXAN CAVE SALAMANDER. 



33 



THE PIGMENT LAYER, EXCLUSIVE OF THE IRIDEAL PARTS. 



The pigment layer is a thin, compact layer, densely pigmented. In an indi- 

 vidual 30 mm. long it is about 8 /a in thickness. As there are no rods and cones, 

 the inner surface of this layer is similar to the outer, that is, the cells form a pave- 



- i. 1 



Fie. s. (a) Right Eye of Specimen of Typhlomelgc 30 mm. long. (6) Exit of Optic Nerve of Same, (c) I 



Eye of Same Specimen, (d) Upper Half of Iris of Right Eye of Specimen of Typliloiiwlge 70 mm. long. 



Tis of Left 



kns 



ment epithelium. In places, however, processes of the cells extend in among the 

 cells of the nuclear layers, for a distance of 40 ^ in some cases (fig. $a), to the 

 inner reticular layer. In the individuals 70 to 90 

 mm. long, the pigment epithelium reaches 16 /x in 

 thickness. The only indication of a lens was found 

 in the eye of a specimen 72 mm. long. In this a 

 small lenticular group of cells lay in the opening of 

 the pupil. It measured 24 x 40 /a (fig. 6). 



THE IRIS AND ORA SERRATA. 



Marked changes take place in the iris from the 

 smallest to the largest individuals examined, so that 

 these must be dealt with seriatim. 



The smallest individual is 30 mm. long (fig. 5 a 

 and c). On the left side the pupil measures 22 [a in 

 diameter; the distance from the margin of the pupil 

 to the ora serrata measures approximately 100 fi. 

 The epithelial part of this iris consists of an outer 

 layer of dense pigment considerably (14 /x) thicker 

 than the pigment epithelium of the rest of the eye. 

 At the pupil this pigment appears rolled into the 

 inner surface of the iris, where it is continuous with the inner layer of cells, which 

 consists of a layer of ordinary pigmentless epithelium 6 /a thick, with the nuclei 

 elongate and placed obliquely, and 24 ti in length. A few of these ordinarily pig- 

 mentless cells show pigment. There is a distinct thickening of the iris at the 

 margin of the pupil. The pigment cells lying on the inner face of this region are 

 much less densely pigmented than those of the outer layer, and their nuclei are quite 

 evident. The pupil is closed with colorless cells belonging to the choroid (fig. 7 a). 



Fig. 6. Lens of Specimen 72 mm. long. 



