OCTOPUS ARM, REGENERATION AND STRUCTURE P| 
flat epithelial cells then proceed to crawl over the wound until 
the latter is entirely covered by an exceedingly thin epithelium, 
which seems almost no thicker than a membrane. The nuclei, 
however, are easily visible and the cuticle shows the characteristic 
striae. I could not detect any nuclear division at this stage. 
Here we have a case of rearrangement of old material, which 
is generally called morphalaxis. Cucagna and Nusbaum found 
that the final healing of wounds in Nudibranchia was accom- 
plished in the same manner. Lang, Hescheler, and Stevens (’06) 
state that the same is the case in worms, but Techow and Hanko, 
who both worked on Gastropoda, claim that mitosis takes place 
in the epithelium while the latter spreads over the wound. ‘The 
cells of the newly formed epithelium vary greatly in shape (fig. 
24). Sometimes they are long, sometimes short and _ broad. 
Some of them are funnel- or pear-shaped, and others again have 
appendages extending into the subjacent tissue. In general 
the epithelial cells are larger than the cells of the adjacent tissue. 
The variety of form among the young epithelial cells is perhaps 
due to the absence of the basal membrane. The absence of such 
a membrane permits the direct connection of the epithelium 
with the subjacent embryonic tissue. This makes it possible for 
cells of this tissue to migrate into the epithelium in order to 
increase more rapidly the rather small number of its cells. But 
in spite of very careful search, [ was not able to find a single 
case of such migration. Wound healing having been accom- 
plished, the epithelial cells, which constitute the covering, undergo 
a change. They no longer remain flat, but become cubical, 
and their nuclei regain their former vertical position, at the 
same time growing more voluminous. At this stage the young 
epithelial cells begin multiplying by means of nuclear division. 
This activity is not confined to a certain part, but spreads all 
over the young epithelium. The division is so rapid that the 
new epithelium is soon filled with a large number of nuclei, and 
on the third or fourth day after operation looks like a syneytium 
(fig. 26a). There are relatively a greater number of nuclei in 
the new epithelium than in the old. As I could not find any 
cases of mitosis, | am inclined to think that the increase in the 
