54 JOHNS HOPKINS UNIVEESITY MORPHOLOGICAL MONOGEAPHS. 



cells, into which the pigment granules happened not to be produced at 

 the moment of fixation. 



Fig. 63, however, where the retina was only slightly pigmented, 

 rather speaks against this view, for the number of darkly pigmented 

 areas seen here (which are shown beyond question by radial sections to 

 belong to the long pigment cells) is not great enough to account for the 

 number of both pigment areas and visual fibres of Schewiakoff seen in 

 such a section as Fig. 64. This would throw the visual fibres of 

 Schewiakoff back upon some of the slightly pigmented cells of Fig. 63, 

 otherwise not distinguished. I think the question cannot be settled 

 without the maceration of fresh material, and experiments upon eyes 

 killed in the light and in the dark. 



In such cases as that of Fig. 63 it would seem conclusively shown 

 that the long pigment cells must belong to a different type from the 

 short, but as I have already said I can find no regularity in either their 

 shape or in the position of their nuclei. And on the other hand Fig. 58 

 shows that the reverse relation may obtain and the long cells be less 

 deeply pigmented on the edge of the retina than their shorter neighbors, 

 so that it looks as if all the short cells had to do was to project half their 

 pigment out into the vitreous body in order to become exactly like the 

 long ones. This they could do if, as is possibly the case, they are pro- 

 longed into "visual fibres" of Schewiakoff that have escaped observation 

 and so do not appear in the drawing. 



Fig. 58 shows one more thing that is worthy of remark in passing. 

 In the preparation in which the vitreous body (at this point at any rate) 

 was not shrunken away from the retina, the fibre from each long 

 pigment cell does not lie in a clearly defined space or " canal," such as is 

 usually described as a constant structure of the vitreous body. Very 

 likely these canals are formed only by shrinkage around the fibres, and 

 the irregular shape of the spaces around the three fibres in Fig. 67 rather 

 bears out the same supposition. 



As to the structure of the vitreous body, apart from the fibres and 

 pigment streaks already mentioned, I find it to be made up of prisms 

 extending from retina to capsule of lens, each containing a central axis 

 or fibre. Fig. 64 shows that the space around the pigment areas and 

 "visual fibres," instead of being homogeneous, is wholly filled with the 

 polygonal cross-sections of these prisms. In Charybdea they are gene- 

 rally more difficult to perceive than in my best material of Tripedalia 

 which was killed in acetic acid. In this the polygonal areas stood apart 



