The Eyes of Dactylopius. 79 



lobes, and also take a course following the contour of the head dorsad, 

 gradually turning mesad to the base of the eye. The lateral eyes are 

 so slightly separated from the lobes as to appear to be lying im- 

 mediately upon them. The nerve can be seen best in the nymphal 

 stages and will be considered later. 



Finally, surrounding the eyes is a thin enclosing membrane in 

 which may be seen at intervals several elongated nuclei. This membrane 

 is composed of cells miich resembling those of the reticulated connective 

 tissue which fills the space between the ventral eyes. And, in fact, 

 Strands from this tissue fuse with the cells about the eye. It is, there- 

 fore, probable that the optic membrane is derived directly from the 

 connective tissue rather than from the neural sheath (Fig. 4, 10, 12). 



Simple as is the structure of the accessory eyes, that of the primary, 

 or lateral eyes is still more so (Fig. 12). Important points of diffe- 

 rence between the two types are, the absence of a corneal hypodermis, 

 the lack of iris cells and likewise the apparent absence of visual rods. 

 The lens in this case is nothing more than a slight thickening of the 

 chitin with an outer convex surface. The fact that no corneal hypo- 

 dermis is present may be due to the small size of the lens, in view of 

 which the neighbouring hy^^odermis is sufficient to form it, or eise keeping 

 in mind the conditions in the accessory eyes, we may regard the layer 

 to have been entirely consumed in the formation of the lens. Since 

 the development of the lateral eyes was not followed this point cannot 

 be definitely stated. 



Beneath this lenticular thickening is a clear vitreous portion in 

 which, at tiraes, there appear to be faint indications of longitudinal 

 lines corresponding to the seams in the visual rods of the accessory 

 eyes. These, however, are probably artifacts and the vitreous body 

 can be safely assumed to be in the nature of a lens which is formed 

 independently of the part described abovc. through a secreticn of 

 the retinal cells and to compose the lower portion of the lenticular 

 body. As in the accessory eyes, there are no rods among the retinal 

 cells. 



The latter are elongate, comparatively large and few in number, 

 there being five to seven in a section. They are so arranged as to 

 form a central depression which is filled l)y the vitreous body. Where 

 the latter adjoins the retinal cells there are to be seen, between the re- 

 spective cells, dark structures similar to those described in connection 

 with the accessorj'' eyes. Covering the cells is a thick mass of black 

 pigment granules. Here too, the nuclei are in the basal ends and 



