STRIPED MUSCLE OF WASP 43 
figures 33 and 44. According to certain investigators (van 
Gehuchten,*! Heidenhain®), the telophragma.is isotropic in 
nature; according to others (Briicke,! Rollet?*), it is anisotropic. 
The weakly anisotropic nature stressed by Rollet, Briicke, and 
Englemann may account for this discrepancy in opinion re- 
garding its physical constitution. 
The literature on the telophragma contains several statements 
to the effect that this membrane is occasionally double. Meigs, 
on pages 87 and 88 of his paper on cross-striated muscle, says 
that in the wing-muscle sarcostyle of the fly “Z itself sometimes 
appears double.” One cannot categorically deny that Z is not 
actually a double membrane, for in muscle fragmented by 
macerating fluids or mechanically the sarcomeres seem to 
separate along the middle of Z; that is, the opposite ends of the 
separating sarcomeres are each bounded by a membrane, the 
result of a splitting of the apparently univalent telophragma. 
It is readily conceivable that under certain conditions such 
splitting of the telophragma has taken place without the com- 
plete separation of the involved sarcomeres. But in well-pre- 
served fibers the telophragma is always apparently a univalent 
membrane. Occasional descriptions of a double nature of the 
Z-membrane may possibly be explained as being based on an 
optical effect due to an oblique position of the sarcostyle or, 
perhaps more frequently, to a slight flattening of the sarcostyle 
under the cover-glass, thus bringing both surfaces of the sarco- 
style into the same focal level, which condition would give the 
appearance of a double telophragma. <A certain number of such 
descriptions of a double Z-membrane may be due also to a con- 
fusion between the contraction band and the telophragma. The 
contraction band is essentially a double structure; occasionally 
both constituents are clearly discernible (figs. 8, 19, 33, and 44). 
When the contraction band has formed, the telophragma is 
usually not discernible; it may simply be masked by the band 
or stretched to a point where it is no longer visible under the 
microscope. Since the contraction band occupies the position 
of the telophragma, confusion between the two and misinter- 
pretation of the double structure at this level during contraction 
may easily follow. 
