128 Victor E. Emmel. 
Examined in section, the papilla is seen to consist of an evagina- 
tion of regenerating epidermal cells. Toward the end of the third 
day after the operation, the regenerating bud has increased consider- 
ably in size (Fig. 10). A characteristic developmental phenomenon 
is that the lateral or outer wall of the bud grows faster than the inner 
or more mesial wall, so that, of the two sides, the outer wall becomes 
both thicker and larger in extent of surface, and contains a greater 
number of mitotic figures and nuclei. It is also on the outer or ven- 
tral sides that the first appearance of joint formation becomes appar- 
ent (Fig. 31). The result of this asymmetrical growth is that the 
regenerating bud bends upward or inward toward the body of the 
animal; a position which evidently reduces the chances for injury 
through friction with external objects. 
It is near the end of the third day, too, that the first differentiation 
of limb segments becomes evident. <A slight groove appears near the 
apex of the bud, and thus marks the first step in the development of 
the two jaws of the claw. It is characteristic that this groove is 
not located directly at the apex of the bud, but is somewhat ventral 
to the tip, with the result that during the earlier stages of develop- 
ment the dactyl is relatively larger than the opposing segment -or 
index of the claw. The fact that this relation in the size of the 
dactyl and the index becomes reversed in the fully regenerated claw, is 
especially interesting since it is a process parallel with the series of 
changes which occur in the normal ontogeny of the claw (Emmel 
06). During the next six days the outlines of the dactylopodite 
and propodite become more definite; the anlagen of all the seg- 
ments appear, and eventually the four joints of the regenerating 
limb become clearly defined (Fig. 31-36). 
As each point develops, an ectodermal invagination arises in rela- 
tion with it. This invagination, which more or less completely sur- 
rounds the joint, soon develops, at two opposite sides of the joint, 
into two proximally directed processes, which are destined to form 
attachments for the flexor and extensor muscles. In the interior 
of each invagination, there is secreted a lamella of chitin which is 
readily demonstrated by its differential stain with Congo red. 
During the development of the joints the epidermal cells present 
