262 The Origin and Differentiation of the Optic Vesicle 
brain tissue remaining attached to the eye by its pigment layer. Or an 
optic stalk may differentiate with the brain tissue at one end and the eye 
at the other. Each tissue seems to continue its own line of development, 
apparently independently of the other, and no distinction is to be observed 
in invagination, or differentiation of the layers of the retina between 
those eyes with and those without attached brain tissue. 
It has already been shown that small pieces of the rudiment of the 
central nervous system possess remarkable powers of self-differentiation." 
The optic vesicle and the brain then stand out in marked contrast to 
the lens and cornea in their power of self-differentiation. Le Cron‘ has 
shown for amblystoma and I have shown in rana palustris and rana 
sylvatica~ that the lens is absolutely dependent on the continued in- 
fluence of the optic vesicle for its origin, early growth, and differentiation. 
The cornea’ likewise lacks the power of self-differentiation and _self- 
origination. 
Among the transplanted eyes there are many very interesting varia- 
tions, in size, shape, and differentiation, dependent for the most part 
upon the amount and distortion of transplantation. Fig. 1 shows a 
large, almost normal, transplanted eye, with quite regular invagination ; 
a lens, endothelial layer, cornea, the pigment layer, and the various layers 
of the retina with the rods and cones are present. The ganglionic layer, 
however, is defective, as its cells are few and scattered, not forming a 
continuous layer as seen in the normal eye (Fig. 2). There are several 
such eyes among my experiments and in some of them an unusually 
large lens (in proportion to the size of the eve), which has retained its 
attachment to the entire inner layer of the retina even long after the usual 
time for the separation, may be accountable for the thinning out of the 
ganglionic layer. Some of the transplanted eyes show just the opposite 
condition and the ganghonic layer may be several cells thick and the other 
layers also thicker than normal. Such eyes show very little invagination 
or very small cup cavities, and as a rule no formation of a vitrous humor. 
And as in the eye of Fig. 5 the invagination may be of such a nature 
that the pupil is entirely obliterated and the cavity reduced to a minute 
space. In Fig. 5 the ganghonie layer is several cells in thickness and 
the outer pigment layer is unduly large in proportion to the size of the 
eve. 
*Lewis, Am. Jour. of Anat., Vol. VII, 1907, p. 138. 
*Am. Jour. of Anat., Vol. VI, 1907, p. 245. 
* Lewis, Am. Jour. of Anat., Vol. VI, 1907, p. 473. 
® Lewis, Jour. of Expt. Zool., Vol. II, 1905, p. 431. 
