120 



THE PINEAL ORGAN 



The epithelium of the now disc-like pigmented area consists of tall, 

 columnar cells which differentiate into basal and retinular cells from 

 which the rhabdomes are formed ; cells which form the lenses, and 

 crystalline cones, and inter-retinular pigment cells. At one end of the 

 area there is a part where cells boundaries are indistinguishable and the 



Fig. 82. — Eye of Acilius Larva. (After Patten.) 



/. ; chitinous lens. 



c. . corneagen, or hypoderm cells, forming the vitreous portion of the lens, 

 optic nerve. p. : pigment. pr. : pre-retinal layer. 



o.n. 



ret. : retina. 



rh. : rhabdomes. 



epithelium appears to consist of a mass of protoplasm containing numerous 

 nuclei irregularly distributed through it ; this is the proliferation zone 

 from which for a considerable time new ommatidia are added to those 

 which are already formed (Fig. 79). The ommatidia consist of two parts, 

 namely, the crystalline cone and the retinula. The crystalline cone is 

 formed by four superficial cells in which clear vesicles appear. The four 



