78 Frederick H. Krecker, 



eye (Fig. 11). Each hexagon represents the cross section of a rod 

 which is therefore to be considered as a polygonal prism of five or six 

 surfaces. In neither longitudinal nor transverse section is there any 

 indication of a subdivision of the rod into smaller elements. 



In addition to the function of sensory cells, the retinal cells also 

 produce the pigment, under a dense mass of which they are hidden. 

 It is composed of numerous, minute spherical granules of a brownish-red 

 color, Avhich in deep layers appear black. They are evidently the 

 2:)roduct of the retinal cells, for no others could be found that would 

 produce pigment, and tlien, too, the granules are most abundant on 

 the retinal cells. This causes the apj)earance of which Beeelese 

 speaks, namely that the pigment is deposited in columns perpendicular 

 to the plane of the lens. These granules fill the entire retinal layer, 

 Cover the proximal portion of the visual rods and, as before stated, 

 are also formed in the ridge surrounding the lens as well as in the iris 

 cells (Fig. 9). Granules, however, were not found in the antennae, 

 asBERELESE tliouglit. The redness of the antennae, which he attributed 

 to this pigment, is found to a greater or less extent, throughout the 

 entire body, and is due to some other cause. The nervous tissue at 

 the base of the retinal cells has no pigment. 



In a depigmented eye one sees great regularity in the arrangement 

 of the retinal cells (Fig. 10). They are long and slender, and are con- 

 siderably wider at their proximal than at their distal end. The cells 

 on the mesal side of the eye are markedly shorter than elsewhere, 

 although there is some Variation throughout the entire eye. The rather 

 large, oval nuclei lie at the basal end. At their distal ends, where the 

 Visual rods arise, the cells are closely applied to one another but an 

 actual grouping of the cells, apparently, does not occur. Immediately 

 below the nuclei the cells are much contracted and are j^rolonged into 

 nerve fibers (Fig. 10 and 7). 



The fibrils from the individual retinal cells can be traced but a 

 short distance before they become lost in the optic nerve. The optic 

 nerves for the several eyes arise independently of each other and are 

 so short and stout as to appear merely like the prolongations of the 

 two elongated lateral lobes of the supraoesophageal ganglion, from 

 which they spring. The two nerves supplying the ventral eyes arise 

 from the ventral surface of the lateral lobes and run for a short distance 

 ventrad and mesad along the side of the head; they then turn further 

 mesad and enter the base of the eye on its ectal side (Fig. 16). The 

 two nerves to the dorsal eyes spring from the dorsal surface of the 



