SPINAL CORD REGENERATION. I 487 
observation are the results of Masius and van Lair (’69), who 
claim that the caudal stump takes little or no part in the re- 
generation of the cord in adult frogs. Brown-Séquard presents 
no evidence as to the origin of the nerve fibers in the regenerated 
area in his pigeons, but states (51), as do Masius and van Lair, 
that the spinal cord resembles a nerve in its method of regener- 
ation. While it is undoubtedly true that the individual nerves 
which make up the cord regenerate in the usual manner, the 
essential differences between the cord and a nerve make an 
exact comparison of the regeneration in the two a dangerous one. 
Though the descending processes of the motor neurones in the 
anterior stump of the cord grow caudad and the ascending pro- 
cesses of those in the posterior piece grow cephalad, they do not 
unite with one another, but pass on to establish their connec- 
tions independently. There is no autoregeneration in Bethe’s 
sense of the term. 
Indeed, it is very doubtful if the term ‘regenerative’ may be 
applied to the nerve development seen in the embryos under 
discussion. There is no degeneration preceding the growth of 
the neuraxes, for no nerves had developed at the time of oper- 
ation. We are, therefore, dealing here with a normal morpho- 
genetic process. The spinal cord as a whole regenerates, the 
neurones do not. 
This fact throws an added importance on the observations 
of the growth of the motor and sensory fibers, as their relative 
time of appearance and point, of origin at the cut surfaces rep- 
resent the nature of their normal development. It is thus 
evident that the descending process of a motor neurone in the 
lower cervical region of the cord begins its development and 
consequently establishes its centrifugal connections before its 
caudally situated neighbor has established its centripetal con- 
nections. It is further evident that the caudally progressing 
differentiation of the sensory tract is brought about by the 
successive additions of cephalically directed axones from the 
sensory cells, not by the development of dendrites toward the 
caudal end of the cord to establish connections with lower neur- 
ones. This confirms the results of Coghill (14) in Amblystoma. 
