56 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



he clear that their distad processes extend to the lens, though he 

 speaks of fibers within the capsule. 



(f) What, now, is the function of these three varieties of cells 

 of the retina? Schewiakoff regards his visual cells (pyramid cells), 

 as the name implies, as having a visual function. That they have 

 such it seems reasonable to suppose, since they have an axial fiber 

 in their pyramids. If the pyramid cells are visual cells, it appears 

 that the prism cells also are such. Indeed, since these are the only 

 ones present in the proximal eye and the more numerous ones in the 

 distal eye, and like the pyramid cells have an axial fiber in their 

 prisms, it seems that they are the visual cells par excellence of the 

 Cubomedusan eye. Also, the analogy between the prisms and 

 pyramids on the one hand, and the rods and cones of the vertebrate 

 eye on the other hand, does not seem to be so far fetched. It may 

 be of interest, here, to briefly consider Patten's theory of color 

 vision. 5 * 3 



The gist of Patten's theory is this : In the eyes of certain 

 molluscs and arthropods, in the parts of the retinal cells corres- 

 ponding to my prisms and pyramids, he not only finds an axial 

 fiber (or fibers) but finer fibrils that extend at right angles from 

 these axial fibers to the surface of the rods (I shall here, for 

 convenience, call the prisms, pyramids, etc., rods) where they probably 

 become continuous with other fibrils in the surface of the rods. 

 These fibrils from the axial fibers are arranged in superimposed 

 planes, and if I understand rightly, an axial fiber with its radiating 

 fibrils may be compared to the axial wire with its radiating bristles 

 of a brush used for cleaning bottles, provided the bristles of such 

 a brush be arranged in superimposed planes. The lateral arrange- 

 ment of the fibrils will, of course, be modified according whether 

 a rod is circular, hexagonal, square, etc., in transverse section. It 

 will also be remembered (p. 49) that Patten describes the retinal 

 cells studied by him as composed of twin cells, and he gives the 

 name retinopkora to a pair. The system of fibers and fibrils in the 

 rods he names a retinidium. Centrad the axial fibers are continued 

 past the nucleus as a nerve fiber. The fibrils extending laterally in 

 superimposed planes from the axial fiber of a rod, Patten supposes 

 to be the ones stimulated by the incoming rays of light, the 

 retinophora being so arranged that the light rays entering them are 

 parallel to the axial fibers or perpendicular to the lateral fibrils of the 



