52 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



polygonal areas differing among themselves in size, but not showing two 

 types of size, or two kinds of pigmentation, the one uniform, the other a 

 ring of pigment around a highly refracting central portion. If the 

 retina is but slightly pigmented and some were so light as to make 

 depigmentation unnecessary a difference is seen in the pigment, as 

 shown in Fig. 63, but in no case were areas found that showed a highly 

 refracting centre surrounded by a ring of pigment. (The unexplained 

 structures in Fig. 63 will be referred to a little later.) 



Figures 59-62 are a series of four successive sections drawn with the 

 camera lucida for comparison with Schewiakoff s Figs. 20 and 19, and 

 to show that the presence of two types of cells plainly marked within the 

 retina by the position of the nuclei at different levels is at least not clearly 

 demonstrated. Only the nuclei are drawn, since the cell bodies are not 

 easily distinguished from the surrounding fibres. The eye is the same as 

 that from which Fig. 72 was made. Fig. 59 shows a relatively small 

 number of nuclei of slightly larger size than usual. These I take for two 

 reasons to be nuclei of the ganglion cells that are found in the fibres at 

 the base of the retinal cells (Figs. 58, gc, 69 and 72). They are the first 

 nuclei struck in tracing sections toward the retina, and in the series from 

 which Fig. 58 was taken similar nuclei appeared in both transverse and 

 radial cuts through the retina stained brightly and clearly with haema- 

 toxylin, whereas the nuclei of the retinal cells proper were stained a 

 diffuse brownish-yellow from pigment that had evidently gone into 

 solution. Fig. 60 shows the closely aggregated, smaller nuclei of the 

 retinal cells surrounded by the nuclei of the outlying ganglion cells. 

 Schewiakoff s corresponding drawing ('89, Fig. 20) shows at this level a 

 definite alternation of the bodies and nuclei of un pigmented visual cells, 

 with the smaller, pigmented, proximal processes of the pigment cells. In 

 the next section (Fig. 61) the pigmented ends of a few of the cells have 

 been struck, and the following section (Fig. 62) shows that, in this 

 heavily pigmented specimen at least, there is no good evidence within 

 the retina itself of two kinds of cells, so that it is apparent that at any 

 rate we cannot accept Schewiakoff s conception of the structure. 



(b) Yet the fibres that Schewiakoff observed and associated with 

 special visual cells occur beyond question. Fig. 6-1 is a drawing of the 

 first cut through the vitreous body of Charybdea, and in among the 

 sections of the pigment streaks are seen sections of processes lying 

 within clear spaces exactly as Schewiakoff figures his visual fibres ('89, 

 Taf. II, Fig. 18). That the fibres occur is indisputable, but as to the cells 



