90 BULLETIN OF THE 



even an advanced stage, the cuticula is so thin that the hypodermis can 

 be studied with comparative ease. An ommatidium from the eye of au 

 advanced embryo is seen in Figure 65 ; the ommatidium is viewed from 

 the side. Distal to the cone (con.) four nuclei can be seen ; one (ill. cm. 1) 

 is superficial in position, three are deep. The relation of these nuclei to 

 the ommatidium can be satisfactorily studied in sections transverse to 

 the axis of the ommatidium. A series of three such sections is seen 

 in Figures 66, 67, and 68. Of these, the most distal is that shown in 

 Figure 66. This includes only the most superficial layer of the retina, 

 and contains two nuclei (compare nl. cm. 1, in Figs. 65 and 66). These 

 nuclei, as their position clearly indicates, represent cells of the corneal 

 hypodermis. In the plane of the section which includes the three deeper 

 nuclei of Figure 65, four nuclei are in reality present (Fig. 67) ; two of 

 these (nl. con.) are large, and lie directly below the superficial ones in 

 the corneal hypodermis; two are small (nl. cm. 2) and lie between the 

 ends of the deeper large nuclei. Of the deep nuclei, the two large ones 

 (nl. con.) rest one above each segment of the cone ; in fact, as a section 

 in a slightly deeper plane shows (Fig. 68, nl. con.), these nuclei coincide 

 so closely with the segments of the cone that they must be regarded as 

 the nuclei of the cone cells. 



It is difficult to state what nuclei in the adult correspond to the 

 smaller of the four deep ones in the embryo. The number of these 

 nuclei (two) in the embryo equals the number of pigment cells which 

 Watase ('90, p. 294) has described as surrounding the cone ; but that 

 these nuclei do not belong to such cells is evident from the fact that in 

 the embryo, the nuclei of the pigment cells can lie identified in a posi- 

 tion somewhat proximal to that in which the smaller of the four nuclei 

 occur (compare nl. dst. in Figs. 65 and 69.) Possibly the cells repre- 

 sented by these small nuclei in the embryo become in the adult the 

 small interommatidial pigment cells, or it may be that they retain 

 their relatively superficial positions, and, while occupying the space be- 

 tween the corneal facets, perhaps produce the cuticula of that region. 

 In the fragments of the adult retina, from immediately below the cor- 

 neal cuticula, small nuclei are not unfrequently met with in the spaces 

 between the ommatidia. These are possibly derived from the smaller 

 deep nuclei of the embryo. 



It will thus be seen that my conclusions concerning the corneal hypo- 

 dermis agree in the main with those of Watase ; namely, that for each 

 ommatidium there are two cells in this layer. Besides these, however, 

 it is possible that the hypodermis may contain an equal number of other 



