48 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



it has been dissolved in from the pigmented zone. The nucleus, 

 again, lies a little centrad from the pigmented part of its cell, so that 

 an unpigmented zone is seen in the retina between the pigmented 

 zone and the row of nuclei (Figs. 4, 7, 22). 



Centrad the prism-cells are continued as a single process (Figs. 

 6, b, c, d, and 8a, b, c, d). In some sections I thought I could trace 

 these processes to the basement membrane, but I could not satisfy 

 myself that such appearances were not due to artificial splitting in 

 the tissue. Schewiakoff makes a similar remark about his supporting 

 cells, which cells I believe are the same as my long pigment cells, 

 but these do not extend to the supporting lamella. 



At the margin of the retina the cells do not develop prisms but 

 remain pigmented and form an iris (Fig. 7), which was so named by 

 Glaus and also described by Schewiakoff. These cells also assume a 

 somewhat different shape (Fig. 6a). This cell (Fig. 6a) is seen from 

 its broader side with which it is applied to the capsule or the lens. 

 Schewiakoff figures similar cells. That the cells of the iris are prism 

 cells without the prisms does not necessarily follow. They simply 

 represent cells of the retinal cup that have become differentiated to 

 serve as an iris. 



As to the exact origin of the prisms, and pyramids (to be 

 described below), it is difficult to say anything definite. If the 

 so-called basal bodies of the axial fibers are really homologous with 

 the basal bodies of flagella, then it would seem that they (the prisms 

 and pyramids) are secretions comparable to cuticular secretions. 



(b) The pyramid-cells, like the prism-cells, are differentiated 

 into three regions: a distal vitreous pyramid, a pigmented part, and 

 a centrad part with nucleus. The pyramids are seen in transverse 

 section in Fig. 1 (pyr) and in longitudinal section in Figs. 4 and 

 7 (pyr).* 



Each pyramid extends between the bases of the prism-cells 

 about one-third to one-half the depth of the vitreous body (Figs. 

 4, 7, 12 (pyr). The pyramids are also a shade lighter than the prisms, 



* In the series from which Fig. 3 is taken the pyramid-cells are not so 

 readily demonstrated. Indeed, I missed them altogether at first in this and 

 some other series and supposed that there were only two kinds of cells (19), 

 but upon a careful re-examination I could demonstrate them to my satisfaction. 

 They did not show, however, in the particular section of Fig. 3, so that they 

 are not indicated in this figure. 



