472 DAVENPORT HOOKER 
stimulation of the posterior part of the body had no effect, but 
direct mechanical stimulation of the muscles of this region pro- 
duced the usual response. 
Sagittal sections of embryos killed at this stage demonstrate 
(fig. 1) that both spinal cord and notochord have been completely 
severed. The epidermis has grown over the wound surfaces in 
such a manner that a partition has been formed across the dorsal 
portion of each embryo, perpendicular to the long axis of the body 
and further separating the severed structures from one another: 
In all but two of the embryos both cord and notochord were 
separated by this ingrowth. In the two exceptions the ends of 
Fig. 1 Sagittal section of an embryo killed 24 hours after operation. The 
- central nervous system is shown in black. The spinal cord and notochord have 
been divided and are separated by a V-shaped ingrowth of epithelium. Embryo 
VIII 81, 2-14). 
the notochord had been sufficiently apposed to reheal, but the 
location of the cut is marked by a deeply staining, dense mass of 
notochordal tissue upon which the epidermal partition rests. 
The epidermis covering the wound is slightly thicker than 
elsewhere on the dorsal surface and lies in almost direct contact 
with the ends of the spinal cord and notochord. It is extremely 
difficult to differentiate between the cells of the cord and those 
of the epidermis. Nevertheless, it seems probable that the 
latter plays no part in the regeneration of the former. This 
tentative opinion is based on the study of a larger series of experi- 
ments than that described in this paper. The investigation of 
this point is not completed but will be published in full at an early 
date. Elsewhere the epidermis is connected to the underlying 
organs by mesenchyme. 
