MUSCLE. 139 
mere optical deception, and that one can never be positive 
with respect to it unless it be observed that the margin in 
question does not accurately follow every bend of the fasci- 
culus. It is, therefore, difficult to be convinced of this in 
mammalia; but in all those larve of insects which present 
the broad transverse strize of the fasciculi, discovered by 
Miller, the membrane, when the continuity of the proper 
muscular substance of a primitive fasciculus has been broken 
at a certain point, may be distinctly observed passing over 
uninterruptedly from the one portion to the other. Pl. IV, 
fig. 4, represents such a fasciculus ; the membrane encompasses 
it so loosely (this larva had been preserved in spirits of wine) 
that a portion of the muscular substance could even change 
its position within the cavity. The membrane, where entirely 
isolated from the other parts of the preparation, shows itself to 
be quite structureless, and, indeed, the sharply-defined ex- 
ternal contour renders it very improbable that it should be 
composed of areolar tissue. I, therefore, consider it extremely 
probable that it represents the cell-membrane of the secondary 
muscle-cell. It thus not only serves to isolate the fasciculi, 
but forms an essential constituent part of them. Pl. IV, 
fig. 5, exhibits this structureless membrane upon a muscular 
fasciculus of the pike; this preparation, however, was not 
quite convincing, inasmuch as the inferior edge of the fasciculus 
was covered by muscles lying above it. By means of this mem- 
brane, the muscular fasciculus remains, throughout its entire 
existence, a cell with a closed membrane and a cell cavity, 
the latter being filled with a firm substance, the peculiar 
muscular substance. It, therefore, clearly follows from the 
above that nervous fibres cannot pass between the primi- 
tive fibres (fibrils) of muscle ; and that the latter cannot 
separate from their fasciculi, so as to pursue a more extended 
and independent course, as is common with fibres of areolar 
tissue ; since, in either case, the cell-membrane must be 
ruptured. 
The true muscular substance, which is thus, in the first 
place, formed as a secondary deposition upon the inner surface 
of the secondary muscle-cell, and continues to be so deposited 
until the entire cavity is filled, is composed in its mature con- 
dition, of very minute longitudinal fibres, the so-called primi- 
