DEVELOPMENT OF THE LENS 



49 



4. A condition intermediate between 1 and 3 in which the elongated 

 hypoderm cells on the sides of the optic cup form a tube of clear refractile 

 cells, having a very narrow lumen in front of the retina. These cells are 

 continuous superficially with the hypoderm cells lying beneath the cuticle 

 and proximally with the retinal cells (Fig. 38). 



5. Mesodermal elements which become included in the dioptric 

 apparatus of the more complex eyes. For instance, the substantia propria 





-rh 



pig. 



"-SC. 



Fig. 35. — Closed Optic Vesicle of Murex, completely separated from the 

 Surface Epithelium by a Layer of Mesenchyme. 



A spherical non-cellular lens of the vitreous type is separated by a space from 

 the sensory cells of the retina. 



c.ep. : corneal epithelium. pig. : pigment. 



cut. : cuticle. sc. : sensory cells of retina. 



/. : lens. rh. : layer of rods formed of parts 



mes. : mesenchyme. of the retinal cells. 



op. n. : optic nerve. 



The clear cylindrical cells lining the vesicle after having secreted the 

 vitreous become differentiated in their inner parts as refractile rods, while 

 their outer parts function as receptive sensory cells. 



of the cornea in the lateral eyes of vertebrates, or in the form of a supporting 

 tissue in the vitreous humour, or accessory structures such as the elastic 

 lamina; of Bowman and Descemet and the capsule of the lens. 



6. A semi-fluid or gelatinous secretion from cells derived from : 



(a) The hypoderm cells or cutaneous ectoderm. 



(b) The retinal epithelium. 



(c) The mesenchyme. 

 4 



