Tissues in the Crustacean Limb. 127 
the size of the nuclei, together with their wider separation during 
migration are sufficient to account for the formation of the first 
epithelium over the injured surface of the limb. 
Similar preliminary regenerative conditions have also been observed 
in other animal forms. Among the vertebrates, Barfurth (790), 
from a study of regeneration in the amphibian tail, concludes that 
the new cells which first cover the wound ‘“‘stammen her vom persis- 
tierenden Epithel der Wundrander, sind nicht etwa durch Theilung 
aus diesen Epidermiszellen hervorgegangen, sondern haben sich aus 
dem Epithelverbande losgelést, sind embryonal beweglich (amdéboid) 
geworden und schieben sich langsam iiber die Wundflache vor, bis sie 
mit den Zellen der anderen Seite Fiithlung gewonnen haben”. The 
process continues until “eine mehrfache Schicht die Wunde bedeckt”’ 
(p. 417). Among invertebrates, Rand (704, p. 39), in his study of 
regeneration in the earthworm, states that “the wound surface becomes 
completely covered by an epidermal layer derived from the existing 
epidermis, without the occurrence of cell proliferation in that layer”. 
V. Tur ForMATION OF SEGMENTS AND JOINTS. 
In this section will be described the earlier stages in the regenera- 
tion of the limb. The description of the further differentiation of 
the tissues and the sequence in which the segments develop is deferred 
to a later section. 
At the time when the first mitotic cell division appears there is 
already present a thin lamella of chitinogenous cuticle formed on the 
outer surface of the epidermal cells (Fig. 9, ch’). The fact that a 
cuticle could be detected as early as the twenty-fourth hour after 
operation indicates that cuticle differentiation may begin before cell 
division has occurred. 
With the appearance of mitosis, there soon follows a rapid accu- 
mulation of cells in the central region of the epidermal disc of cells 
which has formed over the injured surface of the stump. This disc 
of ectodermal cells consequently becomes thicker, its cuticle increases 
in amount, and at the end of fifty hours the regenerating cells (Fig. 
9) are seen pushing outward and breaking through the blood clot 
at the. exterior, to form a papillalike mass near the center of the 
stump. 
