E. W. BERGER ON THE CUBOMEDUS^. 45 



serve as a protection to the prisms of the vitreous portion of the 

 retina during the adjusting movements of the lens. (But more on this 

 below.) To my knowledge all previous observers are quite agreed 

 on the structure of the capsule. Carriers and Haake, however, 

 missed it altogether. 



Retina. While I have enumerated (following previous observers) 

 the vitreous body and the so-called retina as distinct parts, yet, as 

 the sequel will show, they are, histologically, different parts of the 

 same thing namely the sensorium proper of the eye and I propose 

 to use the term retina for both taken together, while I retain the 

 expression vitreous body (as hitherto used) for the vitreous portion 

 of the retina. This simplifies matters ; and using a word that is 

 already used for analogous structures of other eyes (vertebrates, 

 anthropods, molluscs) is conducive to clearness. I have been tempted, 

 furthermore, to use the words rods and cones for the prisms and 

 pyramids that I find in the vitreous bodies of the retinas of the complex 

 eyes. But since the prisms in reality approximate prisms and the 

 pyramids pyramids, in their shape, I have decided to retain the 

 words prism and pyramid for these structures. The former of these 

 terms (prism) was first used by Conant in his description of the 

 complex eyes. 



What I shall call the retina, then, in the distal and proximal 

 complex eyes of Charybdea, consists of three kinds of elements : 

 the prism cells, the pyramid cells, and the long pigment cells. (Figs. 

 4, 7, 22, prc, pyre, Ip.) We may also describe the retina as com- 

 posed of three zones : the vitreous zone (vitreous body of authors), 

 the pigmented zone, and the nuclear zone. (Figs. 4, 7, 22, vb, pz, nz.) 



The cells composing the retina form a single layer in the shape 

 of a hollow cup, into which cup the lens with its capsule fits. (Fig. 7.) 

 This single layer of cells takes in the thickness of the vitreous zone, 

 the pigmented zone, and the nuclear zone. Indeed, the distinctions 

 vitreous zone ( vitreous body), pigmented zone, and nuclear zone 

 characterize three topographical regions of the retinal cells. 



That the retina is made up of three kinds of cells is most 

 readily demonstrated in transverse sections through the vitreous 

 body. Fig. 1 is such a section, taken quite near the pigmented 

 zone (at about the level x, Fig. 4). Three different kinds of areas 

 are readily made out in such a section. The more numerous areas 



