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against the latter, but they still show the same regular outlines. 
The closer study of these extremities of the muscle-plates lining the 
myoseptum, always in thin sagittal or frontal sections through the 
larval body, brings out the following facts. In the first place, as 
mentioned above, the outline of the extremity of the sarcoblast 
remains as clearly defined as before, although now the sarcoblast 
has lost its regular curved outline, but is flattened and broader. The 
extremely delicate boundary-line of the sarcoblast (we may speak 
here already of the sarcolemma) is everywhere to be followed 
with great precision around the entire extremity of the musclefibre. 
In the second place, even when a large number of myofibrillae 
has been accumulated inside the cellbodies of the sarcoblasts, the 
extremities of these myofibrillae where they touch the sarcolemma, 
stand in the two rows of muscle-plates lining the thin layer of the 
primitive myoseptum, always individually exactly opposite each 
other, in this way, that if we follow the line of a fibril of one of 
the muscle-plates through the septum into the opposite muscle-plate, 
we are certain to touch a fibril there with, | should say, mathema- 
tical certainty. | 
As was mentioned above, the myofibrillae arrange themselves 
inside the cell-body of the muscle plates into two flat bundles, leaving 
a median layer of undifferentiated sarcoplasm between them con- 
taining the nuclei. But at the extremities of the muscleplates lining 
the myoseptum the ends of the myofibrillae touching the sarcolemma 
are distributed very regularly over the whole extent of the rounded 
endline of the muscleplates. To attain this regular distribution the 
myofibrillae of the two plate-like bundles have to curve round a 
little at their ends before reaching the sarcolemma, and it is even 
by this fact, that is shown the accuracy with which nature strives 
to place the ends of two opposite fibrils exactly in one line. When 
we prolong the line of such a fibrilla, softly curving round to reach 
the middle of the extremity of the muscleplate, in the same direction 
we are certain to touch with the selfsame curve a myofibrilla of 
the opposite muscle-plate. It is easily understood, that only in this 
manner a regular distribution of the contracting forces and a correct 
cooperation of the contracting forces of the contiguous muscle-plates 
of two myotomes is attained. 
From a histogenetic point of view I would explain it in the fol 
lowing manner, without venturing too far out upon the unfamiliar 
ground of physical theories; we must assume that through the 
dividing layers of sarcolemma and myoseptum (in this stage of 
development only an exceedingly thin layer of gelatinous substance, 
