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for an infolding of the sarcolemma from the periphery of the muscle 
fibre to invest these cells. No definite proof has been ascertained 
as yet that such is the instance in the cardiac fibres. The presence 
of an investment of sarcolemma upon the muscle cells is not, however, 
negatived by this fact. The telophragmata are attached, apparently, 
directly to the external surface of the cell membrane. This fact 
cannot be adduced as conclusive evidence, notwithstanding, arguing 
against the verified observations mentioned above. The matter 
demands further observation upon a greater number of vertebrates. 
Much remains to be studied upon the intermediate genetic steps 
of histo-myogenesis. Sufficient evidence of the presence of myo- 
fibrillae as intra-cellular structures in the first developmental stages 
exists in the literature. In the adult stages of both forms of striped 
muscle, so far as concerns these particular vertebrates investigated, 
these muscle fibrillae are extracellular. A parallelism can be drawn, 
therefore, between myogenesis and developmental sequence observed 
and, seemingly, well established in the case of the connective tissue 
group of structures. At first the connective tissue and the elastic 
tissue fibrillae are intracellular. Later in development they are 
extruded from the genetic cell bodies and occupy, an intercellular 
position. Such is the sequence as well with the striped muscle 
fibrillae. In this fact we can find an additional reason, first, for 
grouping these striped muscle fibres, voluntary and cardiac, among 
the connective tissue group of structures, and secondly, for not con- 
sidering them as multi- or singly-nucleated giant cells. In other 
words the muscle fibrillae and sarcoplasm are inter- or extracellular 
structures. To this extent these observations corroborate those made 
upon the voluntary muscles and detailed in the articles cited. 
The conclusion arrived at, then, is that our conception of the 
cardiac muscle fibre as a cell containing fibrillae and sarcoplasm is 
erroneous as far as concerns the adult white mouse. The terms muscle 
fibre and muscle cell are not synonymous. The cuticular sarcolemma 
invests both the highly specialized muscle fibrillae and the sarcoplasm 
and, in addition, muscle cells. The latter structures present a nucleus, 
cell protoplasm, consisting of a spongioplasmatic network with inter- 
stices of hyaloplasm, and a cell wall. By reason of the last the 
cells are everywhere excluded from the sarcoplasm and the muscle 
fibrillae. | 
