Warren Harmon Lewis 489 
The Size of the Early Stages of the Lens Dependent in Part Upon the 
Area of Contact Between the Eye and Ectoderm. 
Associated with the smallest of the regenerating eyes are the very 
small lens-plates, as in Figs. 15 and 17, or small lens-buds, as in Figs. 
18, 19, 20, 21, 23, 24, ete. Here the area of contact between optic 
vesicle and ectoderm must have been much smaller than in the normal. 
With the somewhat larger regenerating eyes we find somewhat larger 
lens-buds and vesicles, as in Figs. 60, 61, 62, 63, 64, and 65. Still 
larger eyes show larger lens-buds or vesicles, as in Figs. 67, 69, 71, 72, 
and 73. Regenerating eyes which approach the normal eye in size 
have lenses, nearly normal in size, as in Figs. 74 and 76. These differ- 
ences in the sizes of the lenses, as well as in the sizes of the regenerating 
eyes are not due to differences in ages of the embryos, for if cor- 
responding stages in the differentiation of the lens are compared 
it is found that the actual sizes of the lens-plates in small regen- 
erating eyes is much smaller than a normal lens-plate, that the lens- 
buds vary in size somewhat according to the size of the regenerating 
eyes—the lens vesicles also and the early stages of the lens 
proper likewise. In some instances the small sizes are to be accounted 
for by loss of the continued influence of the optic vesicle, as when 
the latter is separated from the lens structure by mesenchyme. These 
differences in sizes are due in great part to the fact that the number 
of cells infiuenced to take part in the formation of the lens-plate and 
lens-bud is probably directly dependent upon the area of contact between 
the ectoderm and the retinal, portion of the eye. In general the area 
of contact will vary with the size of the eye. Owing, however, to 
irregularities in the position and shape of the regenerating eyes it 
might often happen that the area of contact would be either larger or 
smaller than the usual relation of this area to the size of the optic vesicle. 
Hence the size of the early lens is not always in proportion to the size 
of the eye. The lens, for example, in Fig. 73 is larger than in 71 or 
72, but the optic-cup is smaller. The adhesion which normally takes 
place between optic vesicle and ectoderm preceding lens-formation and 
accompanying it is probably an important factor and it is pos- 
sible that without such adhesion lens-formation from the ectoderm 
will not follow. The area of adhesion may not, perhaps, always be as 
large as the area of contact. As, for example, the contact between 
the outer layer of the eye and ectoderm is not followed by lens-forma- 
tion. Whether the outer layer will adhere to the ectoderm or not 
I am unable to say, but presume not, as this would be the most ready 
