REGENERATION IN ANNELID NERVE CORD EE 
regenerated nerve fibers which connect the ganglia in front of, 
and behind the cut, so that normal impulses may pass. Experi- 
ments and observations on the higher forms or in man show that 
when a nerve is cut recovery of the lost function is very slow. 
Does the annelid tissue have a more rapid rate of growth than 
mammalian tissue? I believe not. In the earthworm the ganglia 
lie close together, 0.4 mm. to 0.45 mm. apart. The nerve cell 
processes extend from one ganglion to the next. When these 
fibers are cut the axon to be regenerated is very short, therefore 
recovery is rapid. In regenerating a simple cut, the fibers must 
grow from one ganglion to the next—a distance of 0.4 mm. or 
less. This takes four days, as a general rule, making a rate of 
growth about 0.1 mm. a day. In the nerve regeneration of 
higher forms the part cut is usually a peripheral nerve which 
may have its ending several feet from the nerve cell, conse- 
quently growth from the cut to the ending ‘takes a long time. 
Regeneration has not been successfully brought about in the 
central nervous system, presumably on account of the lack of 
neurilemma sheaths, which, in the case of the peripheral nerve, 
furnish a directing path. In the earthworm the plug, with its 
fibrous connection, forms a path for the developing fibers through 
practically the entire distance traveled. 
Ranson (710), working on peripheral regeneration in the 
sciatic nerve of the dog, has carefully outlined the steps in degen- 
eration and regeneration of the nerve fibers. He reports a 
growth of fibers for a distance of 4 mm. up the nerve and 13 mm. 
down from the cut during a period of twenty-five days. He has 
not worked out the length of time necessary for completion of 
the process and the return of function. This shows a rate of 
growth of 0.65 mm. a day. If such a growth of the peripheral 
fibers of the dog can be compared to the growth of the central 
nervous system of the earthworm, there is here a slower rate of 
growth for the invertebrate than for the vertebrate. 
Thus, although the process of regeneration in the annelid 
appears at first to be remarkably rapid, the early recovery is 
due to the short length of fiber replaced rather than to a more 
rapid rate of growth. 
