474 SHAFER 



None of the sections offers definite proof as to how the group 

 of 7 retinular cells or, of the 4 cone cells, in a single element 

 arise — whether by multiplication of a single mother cell to form 

 each retinula for example, or by association of the original 

 mother cells into groups of cells. The secondary pigment cells 

 however, seem to be homologous or identical with some of the 

 original long hypodermal cells of the first upper hypodermal 

 layer (Fig. 21, A, ihn). The evidence for this is very strong 

 at least, in the young nymph eye of S. corrupta. Fig. 7, A, 

 shows a single developing ommatidia from the unpigmented 

 area of the eye of a young nymph. In this eye, some of the 

 cells of the first hypodermal layer separate into upper and lower 

 parts, the latter giving rise to the retinular layer as in C. hageni. 

 The upper part then becomes two-layered again and cells of the 

 lower of these layers (Fig. 7, A, nfic) become chief pigment cells ; 

 the upper, gives rise to the cone cell layer A, en. Other cells 

 of the first hypodermal layer appear simply to elongate. They 

 grow very little and are seen surrounding the cone, chief pigment 

 cells and retinular elements at A, nsfl. These elongated dor- 

 mant cells lie in the position of the secondary pigment cells in 

 the adult eye. Fig. 7, B, shows 2 elongated hypodermal cells 

 from the developing margin of the eye (Fig. 6, x). They are 

 almost identical in size and shape with what are evidently sec- 

 ondary pigment cells in Fig. 7, A, nsj>. As development goes 

 on, the young short retinulas lengthen rapidly. 



In the 9 mm. stage of development of the Callibaztis nymph, 

 the rhabdomes are found as round rod-like bodies in all the 

 older middle retinulas. By the time the sub-imago is ready to 

 issue, the cones have all practically finished development. A 

 few very small undeveloped cones are found around the outer 

 margin, but most of these remain still undeveloped in the adult. 



Photographs 23 and 25 are made from cross-sections of the 

 heads of sub-imagoes. The turban and lateral eyes are so 

 definitely formed here that one might suppose development 

 complete. Fig. 18, A, shows the structure of 2 ommatidia in a 

 turban eye of a sub-imago of C. hageni. The corneal lens is 

 definite but thin. The retinulas are slightly constricted just 

 beneath the tips of the cones. In the cross-section (Fig. 18, B) 



