Harry Lewis Wieman 201 
The writer’s preparations clearly show that the nodal points of the 
original cyto-reticulum of the embryonic heart cell are marke: by more 
heavily staining deposits, both in longitudinal and in cross section (Figs. 
3, 4, 5, 6). The deposits can be followed in successive stages, and are 
always identified with the longitudinal and transverse threads of the 
network. Eventually they develop into the Querscheibe, and the longi- 
tudinal threads of the network become the axes of the fibril bundles of 
the adult tissue. If this be true, the fibril bundles cannot originate from 
the centers of the meshes seen in cross sections of the cyto-reticulum. 
Suppose now that fibril bundles were to form at the points a and e 
of the diagram. Then we would have the two fibril bundles surrounded 
by one set of sarcoplasmic discs (odtparzhyb), a condition sometimes 
found in the adult; also mentioned by MacCallum, 97 (p. 613), in the 
human heart muscle. However, were these two sets of sarcoplasmic 
discs to become separated by a plane of division along a line from 0 to z, 
then each fibril bundle would have its own set of sarcoplasmic discs, 
the structure more generally met with in the adult. 
If the fibril bundle in its development follows the method suggested 
by the writer, another difficulty is encountered with the results of Mac- 
Callum’s, 98, work. This worker states that the transverse membranes 
of the cytoplasmic reticulum of the myoblasts of man and of pig (repre- 
sented in the chick in Fig. 8, a; Fig. 9, ¢), give rise to Krause’s mem- 
brane in the adult. Attention is called to the fact that (as seen in Figs. 
8 and 9) the intersections of these transverse lines with the longitudinal 
lines of the reticulum mark the positions of the deeply-staining substance 
which later becomes the Querscheibe. Now, in the adult, Krause’s mem- 
brane is found as a narrow transverse band across the lightly-staining 
portions of the fibril bundles, and not at all connected with the Quer- 
scheibe. Thus it is readily seen that MacCallum’s explanation of the 
formation of this structure does not apply in the case of the chick, nor 
could its origin be determined satisfactorily, for, as was remarked in 
another place, it is not very well differentiated in the heart muscle of 
the adult chick. 
At this point it is interesting to consider the work of Eycleshymer, 04, 
on the striated muscle cell of Necturus. This author states that in the 
study of the striated muscle cells of Necturus, he has been unable to 
find any evidence of a definite or fixed relation between the cytoplasmic 
network and the fibrille (fibrils). Further, as serious objection to 
the existence of such a relation, he says that the fibrille are unstriated 
for some time after their appearance. 
