524 S. WALTER RANSON 
After thirty-four days all the medullated fibers in the last 
5 mm. of the proximal stump are transformed into bundles of 
fibers in this way. In Dog vu, in which the nerve was sutured 
and in which therefore the chemiotactic influence of the distal 
stump was brought into full action on the growing fibers of the 
proximal stump, most of the newly formed axons grow directly 
downward into the scar. As is shown in figure 23, the fiber 
bundles are composed of more or less parallel fibers. In Dog 
vil, however, where a piece of nerve was resected and the influ- 
ence of the distal stump therefore was less potent in controlling 
the course of the growth of fibers in the central stump, there 
are more recurrent fibers. Some fibers instead of passing directly 
down the old sheath grow in a spiral direction beneath the old 
neurilemma, producing tangled skeins like that illustrated in 
figure 24, b. The medullated fiber (a) has been transformed 
into a bundle of parallel fibers. These structures are seen in 
cross section in figure 25. In all these bundles and skeins, bulbs 
on the ends of individual fibers are seen and form a prominent 
part of the picture. These two bundles in figure 24 lie side 
by side in the preparation and a small group of fibers can be 
seen leaving Bundle a and running into Bundle b. While therg- 
fore on the whole such a bundle represents the branches of one 
old axon, branches may grow from one bundle into another or 
from a bundle into the endoneurium. Both recurrent fibers 
and tangled skeins are also seen in smaller numbers in Dog 
vit where union of the cut ends favored the action of the chemio- 
tactic influences from the distal stump on the growing axons. 
Fibers with bulbous extremities are very numerous in these ~ 
bundles and skeins. These end bulbs form a prominent part 
of the picture in all the preparations where regenerating axons 
are seen. Cajal has correctly interpreted them as analogous 
to the enlarged extremities seen by many observers on the ends 
of developing nerve fibers and hence ay may be regarded as 
the growing tips of the axons. 
Cajal believes that the tangled skeins arise from the tubular 
networks which appear shortly after the lesion. This, how- 
, ever, does not seem to be the case. They arise from the lateral 
