The Eyes o£ Dactylopius. 77 



specialized and seemed to be more in tlie nature of pigment-bearing 

 liypoderniis cells which liave otherwise altered biit little and can be 

 best liomologized with certain cells in Dactylopius which lie outside 

 of the iris cells and are not a part of the eye proper but form a ridge 

 encircling the base of the lens. These are of a greater size than those 

 of the adjoining hypodermis, are thickly covered with pigment and 

 attain their position through a pushing out of the body wall into a 

 ridge (Fig. •> and 10). 



Turning now to a consideration of the visual rods, they are seen to 

 be in that portion of the eye usually occupied, in numerous ocelli 

 heretofore described, by the cells composing the vitreous body. Since 

 these are the only structures of such a character present in the eye, 

 they doubtless serve both as visual rods and as a vitreous body. A 

 cursory examination suggests the possibility of their being, or at 

 least of their having been originally, a layer of cells. However a study 

 of their development shows clearly that this is not the case; they are 

 an integral part of the retinal cells. Each rod corresponds to a retinal 

 cell from the distal end of which it extends perpendicular to the lens, 

 all of the rods converging towards a common center (Fig. 7 and ]0). 

 They are translucent and slenderly shaped, tapering slightly toward 

 their distal end. The abaxial rods are successively shorter in the di- 

 rection of the periphery, being in a direct ratio to the length of the 

 retinal cells from which they project. Separating the rods from one 

 another is a dark line or seam which is broader at its base than elsewhere. 

 An enlargement of the seam extends about the entire base of the 

 rod where it joins the retinal cell. In structure the seam is composed 

 of comparatively coarse granules which are to be differentiated from 

 the body of the rod mainly by the fact that they stain more deeplv. 

 It is not of a chitinous nature (Fig. 11). 



Just what is the function of these can not be stated with cer- 

 tainty. The longitudinal seams may serve the purpose of preventing 

 rays of light from passing readily from one rod to the other. The basal 

 thickenings remind one of the »lichtpercipierende elemente« in the 

 eyes described by Hesse (99 — 00), but in this instance no nervous 

 connection was found. Similar basal structures are present in the 

 lateral eyes, a fact which would indicate that they might have some 

 sensory significance. 



A cross section through the rod region gives a mosaic of more or 

 less well defined pentagonal or hexagonal areas; a clear central portion 

 enclosed by a dark seam, reminding one of the facets of a Compound 



