E. W. BERGER ON THE CUBOMEDUS^. 57 



retinidium. Again, since the rods are usually the shape of truncated 

 pyramids or cones the lateral fibrils, which are perpendicular to the 

 axial fibers, are of different lengths accordingly as they are situated 

 at the larger or smaller end of a rod. Patten assumes similar fibrils 

 to exist in the rods and cones (particularly the cones) of the verte- 

 brate eye, and he thus makes a general application of his theory. 

 He supports himself in this rather sweeping generalization by the 

 claim to have demonstrated the twin-cell nature of the cones in 

 amphibia and fishes. 



For illustration, Patten supposes that if red light only were 

 admitted to the retinophora this would stimulate the fibrils near the 

 broader end of the cone (but that all the fibrils of the retinidium 

 would be stimulated a little) and that we would thus have the 

 sensation of red light. Likewise, if violet light only were admitted, 

 the fibrils at the narrower end of the cone would be stimulated, and 

 we should have violet light. Similarly, if light including all the 

 different wave lengths of the spectrum were admitted, all the lateral 

 fibrils would be stimulated and the sensation of white light produced. 

 The method of stimulation need not be that of a vibration of the 

 fibrils. 



Certain grave objections may be raised against such a theory, 

 the most serious, perhaps, being the fact that no such fibrils as 

 Patten has described have as yet been demonstrated for the eyes of 

 those animals that we know have color vision. Yet, as a whole, the 

 objections are perhaps no more serious than any that can be brought 

 against other theories of color vision. What Patten's theory does do, 

 it gives us a definite mechanical basis to work from, and if these 

 fibrils should be demonstrated for the rods and cones of vertebrates, 

 physiologists would then have a mechanical basis for color vision 

 quite as they now have for hearing. As Patten says, the problem 

 is primarily a mechanical one. However, the theory cannot well 

 pass for more than a suggestion, a stimulus for future work, and in 

 this lies its present value. 



It is quite evident that my results for the retinal cells of 

 Charybdea are, if any thing, a support to Patten's theory. While I 

 have not been able to demonstrate the fibrils that are the essential 

 to Patten's theory, yet I have demonstrated the axial fibers of the 

 rods, and if these fibers should be continued as a nerve fiber to some 

 central ganglion (as I believe is reasonable to suppose, see p. 47), I 



