Alt — Histology of the Eye of Typhlotriton Spelaeus. 95 



Plate XXVII. — Fig. 3. Vertical section through the head of an adult 

 Typhlotriton. The plane of this section is evidently somewhat oblique. 

 In consequence the left eye shows the eyelids where the small palpebral 

 fissure is open, while on the right side this is closed by firm tissue 

 union of the two lids. On the left the upper eyelid overlaps the lower 

 one in such a manner as to make the palpebral fissure apparently use- 

 less for vision. There is quite a large conjunctival sac. Below are 

 remnants of the food of the salamander. Fig. 4. Vertical section of 

 the head of an adult Typhlotriton. 



Plate XXVIII. — Fig. 5. Vertical section somewhat further back 

 than figure 4. In this specimen no overlapping of the upper lids over 

 the lower one has taken place and there is no palpebral fissure, the 

 lids being united at their margins. The conjunctival sac is plainly 

 visible between the lids and eyeball. Incidentally these sections show 

 the lower jaw and glandular tongue of this salamander. Fig. 6. 

 Vertical section through the eye of an adult Typhlotriton showing 

 under a higher power the manner in which the upper eyelid overlaps 

 the lower one. The cornea and its epithelial covering are well pre- 

 served. The whole eye is evidently pretty firmly united with the sur- 

 rounding tissue and therefore probably immovable. No external eye 

 muscles are visible. 



Plate XXIX. — Figs. 7 and 8. Enlarged from figures 4 and 5, show- 

 ing the union of the eyelids at their margin and the absence of even a 

 microscopical palpebral fissure. Figure 8 shows the capsular epithelium 

 of the lens on its posterior surface. No eye muscles are visible. 



Plate XXX. — Fig. 9. A nearly horizontal section through the eye 

 of an adult Typhlotriton. The crystalline lens lies against iris and 

 cornea; the contents of a possible anterior chamber have disappeared. 

 The thick retina forms a broad band behind the lens from which it is 

 separated only posteriorly by a funnel shaped depression in it cor- 

 responding to the human optic papilla. The inner reticular layer is 

 seen as a white line. There is, also, an indistinct whitish line seen 

 to pass through the thickness of the retina at the posterior pole and 

 apparently to connect with the optic nerve. The latter leaves the eye 

 in a curve and appears darkly pigmented. An indistinct broken line 

 may be seen to separate the two outermost layers of cells from the 

 remainder of the retina. To the right of the optic nerve some mus- 

 cular tissue is seen to insert itself into the sclerotic. Fig. 10. Another 

 horizontal section through the same eye as figure 9. The darkly pig- 

 mented optic nerve can be traced somewhat farther back nasally. The 

 muscular tissue inserting itself into the posterior part of the sclerotic 

 is seen in this section to the right and left of the optic nerve. The 

 small funnel shaped space between the posterior pole of the lens and 

 the retina in both of these figures is filled with an amorphous material. 



Plate XXXI.- — Fig. 11. Enlarged from figure 3. Shows the two lids 

 in the middle of the palpebral fissure and the manner in which the 

 upper one overlaps the lower. To the right is the corneal epithelium 

 cut obliquely. Fig. 12. Enlarged from figures 5 and 8. Although in 

 this eye the lids appear throughout united with each other at their 



