EXPERIMENTAL EVIDENCE IN SUPPORT OF THE THEORY 
OF OUTGROWTH OF THE AXIS CYLINDER- 
BY 
WARREN HARMON LEWIS. 
From the Anatomical Laboratory, Johns Hopkins University. 
WITH 21 FIGURES. 
INTRODUCTION. 
The controversy over the origin and development of the peripheral 
nerves has of late years assumed considerable importance, in ‘that 
vigorous attacks have been made on the neurone doctrine as formulated 
by His, who considered the axis cylinder to be an outgrowth of the nerve 
cell. 
Harrison~ has most successfully controverted the cell chain theory, 
as advocated by Dohrn, and the Hensen theory of an early invisible 
connection between center and periphery, by a brilliant series of experi- 
ments on the larve of frogs, where he proves the axis cylinder to be an 
outgrowth of the nerve cell. 
My experiments given here were not primarily directed towards the 
solution of the outgrowth theory, but I think offer, nevertheless, im- 
portant evidence in support of this theory. 
In transplanting the optic vesicle for the purposes of studying the 
origin of the lens and the development of the eye it often happened 
that a portion of the brain-tube adjoining the optic vesicle was trans- 
planted with it. In experiment Pc,, for example, the optic vesicle and 
an adjoining portion of the neural tube of an amblystoma embryo at 
a stage shortly after fusion of the neural folds was transplanted into the 
region between the optic vesicle and the medulla of another and slightly 
older amblystoma. The transplanted eye and brain tissue have con- 
1The substance of this work was presented to the Association of American 
Anatomists December 28, 1905, and a brief summary is to be found in the 
Proceedings of the Association. Am. Jour. of Anat., Vol. V, No. 2. 
2Wurther experiments on the development of peripheral nerves. Am. Jour. 
of Anat., Vol. V. 
AMERICAN JOURNAL OF ANATOMY.—VoOL. VI. 
