DIVIDED EYES OF CERTAIN INSECTS 473 



below it. These 2 membranes were found also beneath the 

 developing unpigmented ommatidia in the upper eye of young 

 S. corruptee (Fig. 7, A, bm and k, and Fig. 6). The upper 

 membrane is found throughout the further development of the 

 eye and corresponds to the basement membrane of the adult. 

 The lower membrane, k, seems to be identical with the limiting 

 membrane, l\ of the lower pigment cells in the adult eye (Fig. 

 16, A). This second layer of cells (Fig. 21, A, 2/in), then, ap- 

 pears to be that from which developed the lower pigment cells 

 of the adult eye. If that is true, it is clear how it is possible 

 for those pigment cells to migrate up and down through the 

 basement membrane in the adult eye since that membrane is 

 formed, in the beginning, at the inner ends of the outer hypo- 

 dermal layer of cells (Fig. 21, A, ihn), around these developing 

 pigment cells A, zhn, not as an entire or closed membrane above 

 them. 



In cross-sections of the head made at a little later stage of de- 

 velopment, cells of this upper modified hypodermal layer just de- 

 scribed are found to be differentiating into an outer and an inner 

 layer so that 2 rows of nuclei may be seen above those which lie 

 along the basement membrane (Fig. 21, B, if a). Long undi- 

 vided hypodermal cells may still be seen, however, at the edges 

 of this developing turban eye, Fig. 21, B, x, next to the normal 

 hypodermis, and at y, next to the dorsal edge of the lateral pig- 

 mented eye. In a still later stage of development (Fig. 22) the 

 cone cells and the secondary iris pigment cells are found occu- 

 pying the position of the outer row of nucleated cells described 

 in Fig. 21, B, opposite x. The retinulae, each already definitely 

 formed of its 7 cells occupies the position of the second row of 

 nucleated cells in Fig. 21, B, opposite o. Here again the ele- 

 ments in the middle of the developing eye (Fig. 22, ifa) are 

 easily recognized as the older elements. Younger elements at 

 the edges, x andjy, are seen much below the cornea. At each 

 molt of the growing nymph these newer elements at the margin 

 of the eye rise to their normal position under the cornea and 

 thus increase the size of the eye. Fig. 22 represents the stage 

 of development of the turban eye when the nymph is 8 to 9 mm. 

 long. The pigmented eye has practically the same size as that 

 in the 5 mm. nymph. 



