Warren H. Lewis 267 
of brain tissue transplanted with it. The brain possesses considerable 
power of regeneration and when a small piece of brain tissue is cut 
away with the eve the lost part is often regenerated. In some experi- 
ments the brain may show some irregularity without any loss of tissue 
and the transplanted eye is usually large and without any transplanted 
brain tissue. Often, however, the brain is not only shghtly irregular but 
evidently has suffered more or less loss of tissue, the latter having been 
cut away and transplanted with the eye; this defect and the amount 
transplanted may be very slight. Im many experiments there is con- 
siderable asymmetry, showing more loss of brain than can be regenerated 
even after 20 days, and in most of these experiments there is associated 
with the transplanted eye a considerable piece of transplanted brain 
tissue. In none of the 350 experiments, however, was there very much 
brain tissue removed and never any from the other side of the head. 
In some of the experiments the optic vesicle was cut in such a way 
as to leave behind cells enough to form the most proximal portion of 
the optic stalk, that part embedded in the brain.” The brain in such 
cases may or may not be defective and the transplanted eye may or may 
not have brain tissue with it. In many of these experiments the defect 
in the brain is dorsal or anterior to the optic stalk showing that the 
piece of brain transplanted with the eye was from this region rather than 
the ventral optic stalk region. One of these embryos was killed as late 
as 19 days after the operation, yet nothing but the proximal portion of 
the optic stalk had regenerated. 
In some of the embryos the optic stalk is longer and projects from 
the side of the brain, as in Figs. 24 and 25, but has no indicatjon of an 
eve at the distal end. In others a very small knob is to be found at the 
end of the optic stalk consisting of retinal and pigment layer cells (Fig. 
26). Figs. 14 and 27 show very small regenerating eves. I have pic- 
tured regenerating eves of various sizes in a former paper.” Such eves 
vary greatly in size and are often more or less defective in shape. The 
smaller ones show considerable retardation in differentiation and do not 
so often stimulate lens-formation. 
As a rule the larger the regenerated eve the smaller the transplanted 
eve. In many instances, however, the regenerated eye may be two-thirds 
or three-fourths the diameter of the normal eye and transplanted eye 
“Lewis, Am. Jour. of Anat., Vol. VI, p. 493, 1907, Fig. 4. 
* Lewis, Am. Jour. of Anat., Vol. VI, 1907, pp. 495-509, Figs. 7, 8, 9, 10, 
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