Tissues in the Crustacean Limb. Bai 
A careful study of the successive stages of the regenerating bud, 
however, does not warrant such a conclusion. Fig. 9 is typical of 
the conditions found at early stages of the regenerative process. The 
section is taken through the large limb nerve (n”) which is here seen 
passing through a mass of connective tissue (ct). The regenerating 
layer of ectodermal cells (ec) is increasing in thickness. Between it 
and the connective tissue membrane enclosing the nerve trunk, a 
small space has arisen in which may be observed several nuclei 
lying in what seems to be a syncytial mass of cytoplasm. In their 
form, structure, and reaction to stains, these nuclei resemble the 
regenerating ectodermal nuclei. At certain points they are evidently 
migrating directly from the ectodermal layer of cells; and ocea- 
sionally nuclei are seen which seem to be migrating inward from the 
edges of the old epidermis. On the other hand no evidence was 
obtained indicating any proliferation of the old connective tissue 
cells. Mitotic figures were not found, nor did there seem to be any 
migration of the connective tissue cells into the space beneath the 
evaginating ectodermal plate. Occasional blood cells, however, were 
observed within this space. 
Fig. 10 (two days, twenty-two hours) is a section of a regenerating 
bud in which the invagination for the two jaws of the claw has begun. 
The central core of cells is now considerably larger. A few blood 
corpuscles are present in the proximal region of the core, but the 
nuclei of the central mass of cells still resemble the ectodermal 
nuclei. A slight migration of ectodermal cells may be observed 
from the sides of the limb bud, but it is in the region of the invagina- 
tion for the first joint that the migration is most extensive. 
From this advancing invagination the ectodermal cells migrate in 
large numbers, and thus fill the central cavity of the regenerat: 
ing bud. In this central mass of cells mitotic figures were very 
rarely observed. As other limb joints are formed, a similar migra- 
tion of ectodermal cells was found to occur at the invagination for 
each limb segment. No evidence was found indicating the possible 
derivation of these internal cells from the underlying connective 
tissue of the old stump; if it does occur, it seems evident that it 
cannot be to any large degree. This conclusion is based upon (1) the 
