— 43 — 



tinulae (Jietiniilafasern") and ganglion fibres („Ganglienfa- 

 serii"). Dietrich stated without any doubt that in many forms 

 above the granuhir layer seven nerve fibres (the fibres of the 

 retinulae) join into one group. BeloAv this hiyer, in the layer 

 of molecular substance, he finds the same number, but 

 grouped around a smaller number of ganglion fibres; each of 

 the latter begins from one ganglion cell of the granular layer. 

 Bat Dietrich could not decide whether these retinular 

 fibres belong to the same groups, or there has been a re- 

 grouping of them in the interlaying granular layer in the 

 sense that the retinular fibres of one ommatidium are distri- 

 buted among different neighbouring nerve nodes, as it was 

 described by Radl for Squilla. In my fig. 15 the 7 nerve 

 fibres of one „rod'' evidently correspond to Dietrich's re- 

 tinular fibres. According to Dietrich, inside these retinular 

 fibres there must also pass some ganglion fibres the number 

 of which is variable in different species. I did not succeed 

 in discovering them in my preparations. Further details may 

 be revealed only with the help of special methods. However, 

 it is certain— and confirmed by many authors— that the ar- 

 rangement of the fibres in the exterior optic ganglion is a 

 rough repetition of the arrangement of the rhabdom cells in 

 the ommatidium. L o w n e was the first to state that the 

 molecular layer is composed of rods usually united into bund- 

 les which correspond to a separate ommatidium. This corres- 

 pondence in structure between the exterior optic ganglion 

 with that of the retina lead many investigators to regard the 

 former as a component of the retina, and not as one of the 

 ganglia. 



The study of the structure of the exterior optic ganglion 

 inDiopsidae lead me to suppose that there may be a conne- 

 ction between the arrangement of the nuclei of this ganglion 

 and the nuclei of the retinulae. In the retina we find distally 

 a thick layer of nuclei of l — 6 rhabdom cells, and further 

 proximally — a one-rowed layer of elongated nuclei belonging 

 to the 74h cell. A similar arrangement of the nuclei is repea- 

 ted in the ganglion cells of the exterior optic ganglion: 

 distally are situated the densely arranged nuclei of the gra- 

 nular layer, more proximally — a separate one-rowed layer of 

 elongated nuclei, probably corresponding to the nuclei of the 

 7-th retina cell. At any rate, it is remarkable that in other 



