Tissues in the Crustacean Limb. 141 
aspects of the problem, as they present themselves in other animal 
forms, disappear in approaching the subject from the standpoint of 
regeneration. For example, the question whether the fibrils by which 
muscle’ attachment is accomplished are inter- or intra-cellular with 
reference to the epidermal cells, loses much of its significance here 
on account of the syncytial structure of the cytoplasm. Genetically, 
there is perhaps no distinction to be drawn between the purely epider- 
mal fibrils and the myofibrille, for if the conclusions regarding the 
origin of the muscle are correct, both groups of fibrils are derivatives 
of the cytoplasm of epidermal cells, and are consequently also both 
ectodermal. Structurally, however, they have diverged in their 
differentiation, in conformity with their differences in function. The 
striation of the muscle fibril can frequently be traced for some dis- 
tance into the epidermal cytoplasm, but it was not observed that the 
striation of the fibrils ever continues through to the chitin; it appears 
that the peripheral ends of the original myofibrille diffentiate as 
tensile rather than as contractile structures. But even the non- 
contractile elements thus directly concerned with the attachment of 
the muscle to the chitin can be distinguished from the purely sup- 
portive fibrils of the epidermal cells by (a) their staining reaction 
with Congo red and Mallory’s stain; (b) their frequently larger size ; 
(c) their evident continuity with the contractile part of the muscle 
fiber; and (d) their relations with the exoskeleton where they ter- 
minate in characteristic end-plates or chitinogenous processes. 
The conclusions which these observations support may, therefore, 
be summarized as follows: 
1. The myofibrillz differentiate in the cytoplasm of a syncytial 
mass of cells, derived from the epidermis and consequently ecto- 
dermal in origin. 
2. The original fibrille ultimately differentiate throughout their 
whole length into true striated muscle elements, except in the region 
of skeletal attachment, where the peripheral ends of the fibrils remain 
unstriated, and serve as tensile structures directly uniting the con- 
tractile elements with the chitin of the exoskeleton. 
3. In later development connective tissue elements may form over 
the inner surface of the epidermis and around the muscle fibers, and 
