EXPERIMENTS ON THE ORIGIN AND DIFFERENTIATION 
OF THE OPTIC VESICLE IN AMPHIBIA. 
BY 
WARREN H. LEWIS. 
From the Anatomical Laboratory of Johns Hopkins University. 
WITH 32 FIGURES. 
ON THE SELF-DIFFERENTIATION OF THE Optic VESICLE. 
In rana palustris at a time when thesmedullary plate first becomes 
visible, the tissue which later goes to form the eye possesses great power 
of self-differentiation. There is no indication at this time of any histo- 
logical differentiation, in the eye region, between those cells destined to 
form eye or brain; nevertheless, if one transplants a small piece of the 
eye region from the anterior end of such a medullary plate into the 
mesenchyme of the otic region of a somewhat older embryo, the piece 
will continue to differentiate into eye and brain tissue, the various layers 
of the retina, including the pigment layer, will develop and invagination 
will take place. The normal environment then is no longer necessary 
for the continued differentiation of the eye at this period. I have only 
this one preliminary experiment at this stage and none at still earlier 
stages, so it is impossible to determine without further experiment at 
how early a stage the eye becomes self-differentiating. 
My pupil, Mr. Fisher, has found that the eye rudiment at a later 
phase of the medullary-plate stage, in rana sylvatica, when transplanted 
into another embryo possesses the same remarkable power of self-differ- 
entiation. His work will soon be published. 
The present paper is concerned, for the most part, with the differentia- 
tion and regeneration of the eye at a still later stage, at about the time 
of or shortly after the closure and beginning fusion of the neural folds. 
The optic vesicle at this time in both rana palustris and rana sylvatica 
has remarkable powers of self-differentiation. At this stage the optic 
vesicle projects from the side of the brain and produces a bulging of the 
ectoderm on the surface of the embryo." The cavity of the optic vesicle 
SWewaisy Ais OUI. Of Attat. vole wlap. 493, 100K, Kies: 1 25 3:-and: 3a. 
AMERICAN JOURNAL OF ANATOMY.—VOL. VII. 
