138 Victor E. Emmel. 
limb, it is probably due to the rapid growth of the epidermal cells, 
which are consequently forced inward between the muscle fibers. 
After the moult, the regenerating limb expands and the elevations 
then disappear as the epidermis spreads out to cover the now larger 
surface of the limb. 
The muscle fibers appear to be continuous throughout the epi- 
dermis to the chitin (Figs. 18, 19, and 20). Frequently just before 
the fibers reach the chitin they spread out in a brush-like manner 
and fuse with the chitin (Fig. 20). In this fusion the fibrils fre- 
quently terminate on knob-like thickenings or inward projections of 
the chitin (Fig. 19). These chitinogenous processes were found 
only in connection with the attachment of the regenerating muscle 
fibers. 
In later stages of differentiation, the epidermal nuclei adjacent 
to the muscle attachment frequently become considerably lengthened 
in the direction of the long axis of the muscle fiber. In addition 
to the fibrils concerned with muscle attachment, there are other fibrils 
which later differentiate in the cytoplasm of the epidermal cells (Fig. 
19, ef). These latter fibrils do not appear to be associated with 
muscle attachment. In structure they are much finer and are dis- 
tinguished from muscle fibrils by their stain reaction. With Mal- 
lory’s connective tissue stain they appear light blue, whereas the 
fibrils concerned with muscle attachment take a dark red or purple 
stain similar to the striated part of the myofibril. 
On the inner surface of the fully developed epidermis of the 
crustacean there occurs a very thin layer or lamella of tissue which 
has been termed the ‘‘Grenzlamelle” (Schneider). The fact that a 
flat nucleus is occasionally found in this “border lamella” has 
favored the interpretation that it is a connective tissue formation 
and consequently mesodermal in origin. Other investigators (Claus, 
for example) have regarded this layer or “basement membrane,” 
as merely a differentiation of the inner surface of the epidermal 
cells. In regard to this question it is clear that in the early regenera- 
tion of the lobster’s limb there is no definite hmiting membrane be- 
tween the epidermal and muscle cells. The first limiting membrane 
to appear during the differentiation of the epidermal cells is evidently 
