Tissues in the Crustacean Limb. 139 
epidermal in origin and to that extent is ectodermal. This earlier 
membrane seems similar to the basement membrane which MeMur- 
rich (796) describes on the epithelium of the mid gut of isopods, and 
which he coneludes ‘‘was formed from the epithelial cells and not 
by the mesoderm” (p. 89). It is to be observed, however, that at 
a later stage of development (Fig. 21) a thin nucleated layer does 
appear on the inner surface of the epidermis, which is perhaps to 
be regarded as the true “Grenzlamelle.” The origin of this latter 
layer has not been satisfactorily determined. It was noticed that 
it is first apparent in the region of the developing blood sinuses, 
where it appears to serve as a vascular epithelium. 
c. Discussion and Conelusions.—The study of the attachment of 
the arthropod muscle is attended with considerable technical diffi- 
eulty. That the question is still an open one is indicated by the 
diverse opinions existing at the present time. The chief points 
at issue are involved in the solution of the questions whether the 
muscle fibers are attached (1) directly to the chitin of the exoskeleton, 
or (2) indirectly by means of intervening epidermal cells; and in the 
latter case, whether (3) in addition to the epidermal cells there is also 
an intervention of connective tissue between the muscle fibers and the 
epidermis, in a manner somewhat analogous to the muscle attachment 
typical among vertebrates. 
The literature upon this subject is becoming very extensive, espe- 
cially for insects, where the question of muscle attachment has been 
studied by Henneguy (’06), Holmgren (’02), Lecaillon (’07), Riley 
(08), Snethlage (’05),° and others. Without reviewing this grow- 
ing literature, we may advantageously confine our discussion to the 
present observations on the lobster and their bearing on the problem 
among crustacea. 
The third of the different modes of muscle attachment just con- 
sidered involves the union of three sets of fibrils,—the fibrils of the 
muscle, of connective tissue, and of the epidermal cells. Schneider 
(702) is inclined to regard this method of attachment as typical for 
crustacea, and his description of the jaw muscle of the crayfish states 
*Unfortunately, I have been able to have access only to abstracts of Sneth- 
lage’s work, “Ueber die Frage vom Muskelansatze, ete., bei den Arthropoden.” 
