Proceedings of the Association of American Anatomists XI 
Transplanted pieces of the medullary plate possess the power of self- 
differentiation, send out nerves into the strange mesenchyme surrounding 
them or when in contact with the wall of the pharynx may send axis 
cylinders for some distance in among the epithelial cells of the wall of 
the pharynx. 
Injuries to the brain made shortly after the closure of the neural fold 
may form a point of exit for new nerves which may run out into the 
mesenchyme in various directions. Such nerves may arise even anterior 
to the optic nerve. 
The only adequate explanation of such phenomena seems to me to lie 
in the acceptance of the outgrowth theory of the axis cylinder. 
EXPERIMENTS ON THE REGENERATION AND DIFFERENTIATION OF 
THE CENTRAL NERVOUS SYSTEM IN AMPHIBIAN EMBRYOS. 
By WARREN HARMON Lewis. Associate Professor of Anatomy, Johns 
Hopkins University. 
A portion of the dorsal lips of the blastopore transplanted into the 
mesenchyme of a much older embryo of Rana palustris will differentiate 
into spinal cord, notochord and muscle, indicating that the cells of the 
rim of the half-closed blastopore are already predetermined. Small pieces 
of the medullary plate when transplanted into the mesenchyme of older 
embryos likewise possess the power of self-differentiation, and they are 
also able to regenerate a considerable portion of the brain corresponding 
to the region which would normally have developed about the piece so 
cut out. As for example, a small piece from one side of the mid-lne 
and not extending more than half way to the neural fold of that side, 
will regenerate a perfectly bilateral medulla with ventricle, roof and 
typical arrangement of the white and grey substances of the normal 
medulla. Such pieces may also send out nerves along new paths in the 
_ strange mesenchyme surrounding them. 
Embryos from which various portions of the medullary plate are taken 
will regenerate the lost part and a perfectly normal brain will result. 
After closure of the neural folds lost parts of the neural tube are as a 
rule only imperfectly regenerated. 
EXPERIMENTS ON THE ORIGIN AND DIFFERENTIATION OF THE 
LENS IN AMBLYSTOMA. By Wirpur L. Le Cron. Student of Medicine, 
Johns Hopkins University. 
The work of Spemann and Lewis has shown conclusively that lens 
formation is dependent upon the optic vesicle for its initial stimulus. 
Although the lens is not a self-originating structure, the question arises, 
