A428 ROSS G. HARRISON 
small nodule ventral and posterior to the pronephros. In sec- 
tions it is seen to consist of closely packed cells which have 
approximately the same yolk content as those of the normal limb 
on the opposite side and which show numerous mitoses. This 
indicates that after the defect is covered up by inwandering 
of peripheral cells (p. 422), the process of regeneration, like the 
original development of the limb, is dependent upon multiplica- 
i 
Figs. 10 and 11 Embryos with regenerating limb buds, ventral view. x10. 
R, regenerating limb; N, normallimb. Figure 10. Experiment R. E. 127—,' six 
days after operation. Figure 11. Experiment R. E. 129—, fifteen days after 
operation. 
tion of cells in situ rather than upon the continued crowding 
together of cells from the surrounding regions. The ectodermal 
covering of the new limb bud, as well as that of the original 
one, is considerably thicker than the ectoderm of the neighboring 
region of the trunk. 
A case (R. E. 115—) preserved at nine days shows similar 
conditions, though further advanced. Nerve fibers from two 
spinal nerves may be traced to the base of the regenerating limb. 
