Warren H. Lewis 263 
Some of the transplanted eyes are very irregular in shape, owing to 
absence of or irregularity in the invagination, due to distortion in trans- 
planting. Figs. 3 and 4 are from an eye where invagination failed to 
take place. Fig. 3 from a section very near one end of the eye shows 
only a small area of pigment layer, the larger part of the eye is entirely 
without a pigment layer and forms a flattened ‘vesicle, the walls of 
which are composed of the various retinal layers with the rods and cones 
lining the cavity (Fig. 4). Figs. 8, 16, and 18 show very irregular 
eyes." In these the distortion of the vesicle at the time of transplanta- 
tion was probably too great to be overcome by any regulative mechanism. 
In these as in Figs. 3 and 4 and in others the arrangement of the various 
layers of the retina is so irregular as to suggest the idea that at the 
time of transplantation there is already a determination of the various 
cells which go to form the several lavers of the retina and they seem to 
continue along this predetermined path of differentiation in spite of the 
alteration of their position in the eye, so that those destined under 
normal conditions to form rods and cones, for example, do so in the dis- 
torted eyes and thus, as in Fig. 3, small groups of rods and cones r, r, 
are found separated off from the rest of the layer. In Fig. 29 a similar 
small group of rods and cones is seen in the center of the inner granular 
layer.” 
The small extent of the pigment laver in some eyes as in Figs. 3 and 
4 or its excessive extent as in Fig. 5 suggest that at the time of the 
operation the cells which go to form the pigment layer are likewise 
already predetermined, and so, if but a few are transplanted with the 
eve this laver is scanty, while on the other hand, in some transplanted 
eves, the proportion of cells destined to form pigment layer to those 
destined to form the other layers of the retina may be so large as to give 
rise to eyes with a great excess of the pigment layer as in Fig. 5. This 
predetermination in the fate of the cells seems to be borne out by the 
finding occasionally in the mesenchyme small detached groups of pig- 
ment cells of the same character as those in the eye. Such groups prob- 
ably owe their origin to bits of detached optic vesicle which were broken 
away at the time of the operation. Small pieces of retina were also found 
(see Fig. 6), but here a small mass of pigmented cells is connected with 
it. Other pieces show only retmal cells without any pigment. 
Under certain conditions invagination may fail entirely and the eve 
See Wigs. 2, 6, 8; 17, 19, 28, 30, 40, 41, 49, 55, 56, 57, and 59, Lewis, Am. 
Jour. of Anat., Vol. VII, 1907, pp. 153-167. 
See also Fig. 44, Lewis, Am. Jour. of Anat., Vol. VII, 1907, p. 163. 
