122 Victor E. Emmel. 
characteristics of a nucleolus. Whether the presence of nucleoli is 
typical of this stage is, however, questionable, for with the same stain 
they can also be found, although less frequently, in the normal or 
resting nuclei. 
The nuclei shown in Fig. 13 are from a limb fixed twenty-four 
hours after autotomy. At this time the migrating epidermal cells 
have progressed considerably in their advance over the surface of the 
stump. ‘The nuclei drawn are from the same specimen as are those 
of Fig. 12, but they have been selected from a region where the 
advancing epithelium has already partly closed over the inner side 
of the stump. As the epidermal nuclei migrate, their long axes 
rotate through an angle of about 90 degrees from their former posi- 
tion, and in such a way that at the center of the stump the long axis 
of the nucleus assumes a position practically parallel to the long axis 
of the limb (Fig. 8). In Fig. 13 the nuclei ¢ and d are nearer the 
center of the stump. As the nuclei approach the central region, there 
is an increase in their shortest diameter, giving each nucleus a broader 
and less elongated form. They now also become more widely sepa- 
rated from one another. In the earlier stages of migration the lower 
or proximal ends of the nuclei tend to assume a tapering or pointed 
form. 
A striking structural characteristic is the unequal distribution of 
the chromatic material (giving the nuclei a “loaded” appearance). 
The proximal end of each nucleus takes a relatively deep stain, while 
the upper or distal end of the nucleus is so pale that frequently little 
or no stain can be detected except in the few scattered granules of 
chromatin. In nuclei a, 6, and d, one can see that the boundary be- 
tween the light and dark areas, or zones, lies at such an angle across 
the nucleus that the darker zone occupies the lower and left region, 
and vice versa for the lighter zone. The nuclear contents have much 
the appearance of having been centrifuged. In nucleus ¢ the plane 
separating the two zones is more nearly equatorial in position. It will 
also be reealled that these nuclei were taken from the left side of the 
section of the limb (¢ being nearest the center of the limb), In nuclei 
taken from the opposite or right side of the same section, it is inter- 
esting to find the localization of the two zones just reversed, 2. ¢., the 
