83 



and possibly is the seat of formation of the blood 

 corpuscles. This, however, is doubtful, as its blood 

 supply, from the arteries of the eye, is very limited. 

 The skin which covers the eyelid, after being reflected 

 over the pseudo-corneal membranes, is continued down 

 the inner surface of the external muscular coat of the eye 

 (fig. 78, Conjunct.). Just anterior to the cartilaginous 

 capsule it is reflected on to the globe of the eye, and 

 running up clothes the iris as far as the pupil. Here it 

 is again reflected internally and runs down on the internal 

 surface of the iris, and then over the ciliary body, and 

 then is continued as the external layer of the true cornea. 

 This outer layer of the two-layered cornea thus arises 



D: 



Fig. VI. Diagram showing relation 

 of white body to eye and optic 

 ganglion, x 1. 



W.B- 



from the infolded external skin of the head, while the 

 internal layer is the external part of the wall of the optic 

 vesicle, of which the internal part forms the retina. 

 Hence the internal layer of the cornea and the retina are 

 continuous. The two corneal membranes secrete the lens 

 which thus is in two segments, an external smaller one 

 and a larger internal. The external division is a 

 segment of a much larger sphere than is the internal, but 

 the two themselves are of equal area where they adjoin 

 the cornea. They readily separate. The internal 

 segment alone corresponds morphologically with the 

 Gastropod lens. The rest of the ocular cavity is occupied 

 by the vitreous body — a thick, perfectly clear and 

 transparent fluid, contained in a thin membranous sac 



