Eyes of Molluscs and Arthropods. 641 



foUowed out to the pigmeuted ends where. ou account of their exces- 

 sive fineuess, they disappear. The nerve fil)res of the retinulae 

 cling elosely to the wall of the cell, which they follow as far as the 

 nucleated portion. where they become confused with those of the outer 

 wall of the retinophorae. Those of the latter are the most important, 

 and may be traced aloug- the outer walls of the retinophorae, surround- 

 ing the style and pedicel with a uumber of long-itudinal tibres continued 

 outward over the surface of the calyx (fig*. 71 ex.n.f.). The axial 

 nerve extends from the base of the retinophorae, through the pe- 

 dicel and the central canal of the style (figs. 70 ax.f^^ into the 

 calyx, between the four Segments of the crystalline cone. In cross sec- 

 tion, it is most easily seen at either end of the pedicel (fig. 94 — 96), or 

 in the lower parts of the calyx. The conditions for the study of the 

 ramifications of the axial fibres to form the retinidium in Penaeus are 

 not favorable, and therefore my observations in this respect are not as 

 complete as I desired. Still, one may see enough to be convinced that 

 the sanie principle prevails here as in Mantis. Those parts of the calyx, 

 not occupied by the crystalline cone, or by the lateral thickenings, seem 

 to have been filled with a fluid, in which probably existed a network 

 of nervous fibrils, similar to those forming the retinidium in Area and 

 Haliotis. One may find positive evidence of it, however, in the fact that 

 the lateral thickenings are marked with extremely fine , and nearly 

 straight, cross lines,which I consider to be parts of the retinidium, better 

 preserved by being imbedded in the more compact substance of the 

 lateral thickenings. Moreover, in the softer portions of the crystalline 

 cone, the same structure may be seen (fig. 79 and 80). It is therefore 

 probable that the whole space enclosed by the outer walls of the four 

 retinophorae, or the cavity of the calyx, is tìlled with a mass of radiat- 

 ing nerve fibres, which are better preserved in those places where thc 

 substance filliug the calyx has hardened to form the lateral thickenings, 

 or the centrally placed crystalline cones. It is also probable, from 

 theoretieal considerations , that the system of superficial fibres , distri- 

 buted over the wall of the calyx, communicates with the cross branches 

 from the axial nerve, just as in Pecten and Area. In the outer ends 

 of the crystalline cone, in that part which is densest and most hyaline, 

 I have not been able to observe anything like cross lines or fibres. 



Galathea, Palaenion and Pagurus. 



After completing my observations upon Penaeus, I desired to make 

 similar studies upon typical genera from the various families of Crus- 



Mittheilungen a. d. Zoolog. Station zu Neapel. Bd. VI. 43 



