— 44 — 



D i p t e r a, where one-rowed layers of nuclei are often found 

 in the retina, such a repetition in the distribution of the 

 nuclei of the exterior optic ganglion is not to be observed. 



All the layers mentioned till here are convex and extend 

 parallel to the curve of the basilar membrane. 



Proximally to the molecular layer, in the white cerebral 

 substance Ave still find separate dispersed nuclei of the gang- 

 lion cells which, probably, correspond to the last layer of the 

 exterior optic ganglion — the layer of ganglion cells („Gangli- 

 enzellenschicht") of B e r g e r. 



After the exterior optic ganglion follows crossing of the 

 nerve fibres — the „chiasma" (fig. 3, ch), which joins together 

 the exterior and interior optic ganglia. 



In the interior optic ganglion (fig. B. G o. i.) are situated 

 two transversely arranged, semilunar complexes of ganglion 

 cells w^hich are not densely distributed: one — distally, the 

 other — in the middle. On the periphery of this ganglion the 

 ganglion cells are very densely arranged. A more detailed 

 analysis of the structure of the optic ganglion would be beyond 

 my task. 



The Double Eyes. 



As we have seen in the preceding paragraphs, one part 

 of the lateral eye of Diopsidae, namely — the anterior, has 

 undergone a special modification with respect to the elements 

 composing it. This part is distinguished from the rest of the 

 eye by the following peculiarities. The ommatidia of the an- 

 terior area of the eye are nearly twice larger than the remai- 

 ning ommatidia, they are arranged nearly parallel and their 

 base, the basilar membrane, is not convex, but plane. In the 

 dioptric apparatus both the facets, and the pseudocones are 

 enlarged. The form of the facet of the cornea is wide and 

 flat concavo-convex, and not plano-convex. The receptive ap- 

 paratus is also increased. The retinulae with the rhabdomeres 

 are considerably elongated, but are not accordingly wider; on 

 account of this, they are further from each other and are 

 adjacent only by means of pigment bridges of the retinal 

 pigment. The retinulae of the anterior area of the eye are also 

 distinguished by a specially narrow axial cavity in which the 

 rhabdomeres are set very close to each other. Their retinal 

 pigment is developed stronger. 



