STRIPED MUSCLE OF WASP 49 
There is one illustration that calls for an explanation in this 
connection. It is figure 71 by van Gehuchten*®! (’86) which 
shows a bisected anisotropic disc, corresponding to the midphase 
of contraction as represented in stained preparations. If the 
anisotropic substance does not divide and move toward the telo- 
phragma to help form the contraction bands, as van Gehuchten 
himself supposed, how, then, is this illustration to be inter- 
preted? Two explanations suggest themselves, neither, how- 
ever, wholly satisfactory: 1) it may represent a variation of the 
more regular stratification when present or, 2) it may be of a 
fiber stretched at an early stage of contraction in such manner 
that the anisotropic substance has actually become divided. 
But quite aside from the erroneous assumption of a strict 
spatial correspondence between an anisotropic ‘substance’ and 
the Q-dise of the stained fiber, entirely too great relative im- 
portance has been ascribed to this anisotropic substance in 
relation to the phenomenon of contraction. In the first place, 
it may again be emphasized that many non-contractile sub- 
stances, both inorganic and organic, are anisotropic. Con- 
tractility cannot be regarded as a function of anisotropy. More- 
over, as Ranvier” long ago showed, anisotropy itself is a function 
of the uniform direction of stress. He showed that india rubber 
in the usual condition is isotropic, but when stretched it becomes 
anisotropic. He summarized the results of his studies on this 
subject as follows: ‘““Monorefringent bodies become birefringent 
by virtue of a modification in their molecular state, without 
change of composition . . . . a body becomes birefringent 
when its molecules are oriented in one and the same axial 
direction . . . . muscle has the same structure in repose, 
extension and during return to repose . . . . only the 
length of the structures varies—inversion of striae does not 
exist.”’ 
There would seem to be a parallel between the different 
optical conditions of the india rubber in repose and extension 
and the contracted and relaxed (or extended) muscle fiber. A 
similar phenomenon of alteration in optical conduct of a homo- 
geneous substance under stress is exhibited by glass when put 
