E. W. BERGER ON THE CUBOMEDUS^J. 59 



cesses. These facts suggest that they are not sensory but the center 

 of a reflex mechanism.* When the sensory cells proper are stimulated, 

 the impulses are conducted centrad into some nerve center (it may 

 be the nerve tissue underlying the retina, or other nerve centers such 

 as the two groups of ganglion cells in the upper part of the club, or 

 the radial ganglia) from which center, again, impulses return over 

 fibers leading to the long pigment cells causing them to project their 

 pigment, and conducting the impulse to the lens, to produce a change 

 in its adjustment. Since these cells are not so numerous as the 

 prism and pyramid cells taken together, but in turn have a number 

 of processes continued centrad (the sum of which processes approx- 

 imates the number of sensory cells, prism and pyramid cells) it 

 appears that these cells are admirably adapted to function in just 

 such a mechanism as I have described, each long pigment cell 

 serving a number of its immediate neighbors. 



Further, we may conceive each of the centrad processes of the 

 long pigment cells as receiving a fiber from one of the sensory 

 cells directly as well as indirectly, as just described. While I 

 have been able to demonstrate only a single centrad process for the 

 sensory cells (prism and pyramid cells), yet this does not exclude the 

 possibility of a nerve fibril passing out from such a centrad process 

 to one of the processes of the long pigment cells, and it seems 

 possible that this constitutes the reflex mechanism. That nerve fibrils 

 ramify in ganglion and sensory cells, and may even leave these cells 

 to join those of other cells, has been well demonstrated by Apathy, 1 '' 

 so that my finding only a single process of the visual cells leading 

 centrad without giving off lateral fibers cannot be a serious objection. 

 Again, fine nerve fibers coming off from the main centrad process of 

 sensory cells in medusae have been figured by other observers, among 

 whom I mention the Hertwigs. Careful macerations at the seashore 

 would probably demonstrate them for Charybdea. 



Hesse thinks that the eyes of the Alciqpidas are adjustable. He 



*It may be objected that my criterion, the presence of axial fibers, is not 

 necessarily characteristic of visual cells. However, the great general occurrence 

 of such axial fibers (Patten, 5 Grenadier, 1 '' 1 Schreiner, 1 ' 2 Hesse, 13 myself, in simple 

 complex eye, see below, and perhaps others) in eyes in which the retina has 

 only one kind of cells, would seem to indicate that they are quite character- 

 istic of visual cells. Note again that in the proximal eye of Charybdea there 

 is only one kind of cells and with axial fibers. 



