Tissues in the Crustacean Limb. 191 
fused into a true syncytium. Indeed, Huxley’s description of the 
epidermal epithelium of the crayfish apples equally well to the lob- 
ster,—‘‘It is found to consist of a protoplasmic substance in which 
close set nuclei are embedded . . . there can be no doubt that 
it is really an aggregate of nucleated cells, though the mits between 
the individual cells are rarely visible in the fresh state” (p. 178). 
It may be added that in the lobster at least, cell boundaries are no 
more clearly defined even after fixation and staining. In view of 
these facts it becomes evident that in making observations upon cell 
changes in such a tissue, attention is necessarily more largely directed 
toward the nuclei of the tissue cells. 
The characteristic structure of normal epithelial nuclei as they 
appear immediately after the autotomy of the limb is shown in Fig. 
11. They may be described as more or less elongated or oval in 
form with a clearly defined nuclear membrane. A structural charac- 
teristic is the segregation of the chromatin into relatively large angu- 
lar masses or karyosomes. ‘These karyosomes take on a heavy stain 
with hematoxylin, and are rather evenly distributed throughout the 
periphery of the nucleus. ‘The ground substance stains a uniformly 
light color. The four nuclei in Fig. 11 were from the epidermal 
epithelium just below the breaking plane and from a region at the 
inner side of the basipodite near the limb nerves. 
Fig. 12 represents epidermal nuclei fourteen hours after autotomy. 
To facilitate a more direct comparison of structural characteristics, 
these nuclei were taken from practically the same region as the nuclei 
shown in Fig. 11, 2. e., from the inner side of the basipodite,—a 
region of the epidermis where regenerative activities are first ob- 
served. Of these four nuclei, a and b are proximal of ¢ and d and 
farthest from the region of the first regenerative changes. In con- 
trasting c and d with a and b, and also comparing with Fig. 11, it 
may be noticed that the nuclei are becoming larger in size and the 
chromatin is undergoing certain changes. In a and b the karyosomes 
are still large and are similar to those in Fig. 11. But in ¢ and d 
the chromatin is more finely subdivided and arranged in a reticulum 
of chromatin strands and knots. In nuclei a and ¢ a round, centrally 
located body is seen, which takes a relatively lighter stain and has the 
