AMPHISB^NA. 



43 



lens 



ing at present or not. In each specimen examined the eyes appeared in about 

 the same state of degeneration. 



The eye measures 1,224 /* in circumference and the pupil 104 jx in diameter. 

 The uveal part of the iris on each side of the pupil measures 250 /x. The pupil 

 and iris occupy 49.3 per cent, or very nearly half, of the entire circumference. 



Harder's gland is very much larger than the eye. In a cross-section through 

 the central part of the eye, the antero-posterior diameter of the gland is approxi- 

 mately three times and the medio-lateral diameter four times the medio-lateral 

 diameter of the eye. It is divided into two distinct lobes, the anterior being much 

 smaller than the posterior. The gland completely surrounds the eye except over 

 the anterior face. Its secretion is poured into the conjunctival sac and from 

 thence into the mouth cavity. The large size of the gland in Typhlops led 

 Duvernoy to the conclusion that its function was not connected with the eye. 

 As its secretion, in Amphisbcena, is 

 poured into the conjunctival sac and 

 thence into the mouth cavity, its 

 function must have been, primarily at 

 least, connected with the eye. No eye 

 muscles are present in Amphisbcena. 

 The eye is directed outward and for- 

 ward and makes an angle of about 6o° 

 with a line drawn tangent to the 

 dermal plate which covers it. 



Whether the eye is still used as a 

 sense-organ is not certain, but since 

 the parts are so well developed and 

 the eye is not buried very deeply 

 beneath the surface, it is probable that 

 it is at least susceptible to light. 



The Sclera. — The sclera (scl., fig. 



14) haS apparently Undergone nO Fig. 13. Diagram of Eye, showing Parts in their Relation and Dis- 

 , ' . x 1 . _, ° tance of Eye beneath Surface. 



degeneration whatever, it compares 



favorably with that of Anolis. In 



fact, there is but little difference in its 



structure in the two eyes. At the 



proximal part of the eye, the sclera measures 12 fx in thickness, while at the same 



place in Anolis it measures 15 /x. It is continuous over the front of the lens as the 



cornea, which together with the thin wall of the conjunctival sac at this place 



measures 7 jx. Scleral cartilages extend from about the middle of the eye back 



almost to the optic nerve. On each side of the sclera, and forming a part of it, 



are thin irregular layers of pigment in patches. 



MINUTE ANATOMY OF THE EYE 



The Choroid. — If the blood-vessels in the choroid still persist, the preparations 

 do not show them. All that can be seen is a number of densely pigmented cells, 

 around and between which are filaments of connective tissue (chr., fig. 14). At the 

 entrance of the optic nerve, this layer measures 8 /x in thickness, but gradually 

 becomes less forward and vanishes entirely a short distance back of the enlarged end 

 of the pigment layer. The pecten, present in Anolis, is not seen in Amphisbcena. 



, pigment layer; 2, cones; 3, outer nuclear layer; 4, outer retic- 

 ular layer; 6, inner nuclear layer; 8. inner reticular layer; 0, 

 ganglion-cell layer; 10, fiber layer; lens, lens; scl., sclerotic; 

 chr., choroid; cor., cornea; scl. c, scleral cartilage; n. op., 

 optic nerve; vit, vitreous cavity; con. cav., conjunctival cavity; 

 C, outer covering of eye; M., Mullerian fiber; L. t membrana 

 limitans externa. 



