SPINAL CORD REGENERATION. II 429 
dermis and the cord ends as the former is withdrawn, so that 
the only connections remaining between the two are mesen- 
chymal in nature. The only time at which the epidermis could 
contribute elements to the spinal cord is in the earliest stage. 
While it is not possible to definitely state that no such ele- 
ments are contributed, the continuity of the epithelial tissue and 
its separation from the cord ends cast strong doubt on such a 
condition. The mesenchymal elements which become mixed 
with the developing nerve fibers are cast out at a later stage 
by the development of ependymal cell fibers and the wandering 
out of neuroblasts in the same manner as has been described for 
embryos with severed spinal cord. 
In embryos having the cord merely cut in two, the first active 
regenerative process which is visible is the growth of nerve fibers 
from both stumps of the cord. From the cephalic stump (fig. 3, 
I, A) in such cases, there appears a number of rather large nerve 
fibers which grow toward the caudal stump. These fibers are 
the descending processes (A, dm) of motor neurones situated 
within the cord cephalad to the cut. They are the first fibers to 
appear at the wound surface. From the caudal stump (fig. 3, 
I, B) there appear shortly after the outgrowth of motor fibers 
from the cephalic stump, bundles of fibers which are the ascend- 
ing processes of motor neurones situated caudad to the cut 
(B,am). At a slightly later time, a number of small nerve 
fibers appear from the caudal stump growing out from its dorsal 
portion toward the cephalic stump. These fibers are the as- 
cending processes of the sensory neurones (B, ds). No sen- 
sory fibers could be identified as such, growing from the cephalic 
stump. ‘They appear to be very essentially centripetal in their 
manner of growth. 
In embryos having the cord cut in two places, without reversal 
of the piece between the cuts, a condition represented in figure 3, 
If obtains. There are four cut surfaces, C, D, H and F, of which 
Cand F are true cephalic stumps of the cord, corresponding to A 
in number I of the same figure, and D and F true caudal stumps 
corresponding to Bb in I. The regenerative conditions found in 
the wound CD are identical with those in the wound AB in I, 
