STRIPED MUSCLE OF WASP Di 
|= 
Hensen’s me- i 
dian disc. \V 
Sarcostyles. 
B. 
Krause’s 
membrane. 
Sarcomere. 
Sarcous ele- 
ment. 
Sarcoplasm. 
B, 
Fig. 9 Diagrams to illustrate the phenomenon of contraction in voluntary 
striped muscle (A and B according to Schaefer; C has been added by the writer). 
According to Schaefer, diagram A illustrates two relaxed, ‘moderately extended,’ 
sarcomeres; B, two contracted sarcomeres. During contraction the isotropic 
substance of the light dise is supposed to become absorbed by the anisotropic 
substance of the dark disc, thus producing a shortening and thickening of the 
fiber. To bring these diagrams into agreement with Schaefer’s illustrations of 
wasp’s wing muscle (fig. 6), upon which they are based, A and B must be regarded 
as single sarcostyles (not six myofibrils) each with five ‘pores’ through which the 
‘hyaline’ lightly staining substance passes into the deeply staining ‘sarcous’ 
material of the dark dise. The writer has added diagram C to illustrate his 
conception of the contracted fiber (with six myofibrils; or a sarcostyle with six 
metafibrillae). Disregarding the exaggerated length of the two sarcomeres in 
A, he would interpret the three diagrams as illustrating the relaxed condition 
of the fiber in B; the beginning of contraction (since the median disc has made 
its appearance), in A; and the condition of full contraction, with contraction 
band, C.B., in C. The terminal knobbed condition of the ‘myofibrils’ in B is 
regarded as showing the passage of the deeply staining constituents of the dark 
disc toward the telophragma, not the passage of a substance in the opposite 
direction, as Schaefer would have it. If the contraction band were really the 
result of a relative condensation and consequent darkening of the J-substance 
about Z, due to a flowing of lightly staining substance into Q (thus producing a 
relative rarefaction in Q), then the Q-dise should become lightly staining ter- 
minally before it clears up centrally, which is the exact reverse of actual con- 
ditions (A; and figs. 2 and 3). 
and diagrams of Schaefer, are unsatisfactory. Before we. can 
arrive at a correct conception of the intimate mechanism 
of muscle contraction, the detailed morphologic basis of this 
phenomenon must be definitely established. In the following 
pages it will be my chief aim to show that wasp’s wing muscle 
passes through the same series of morphologic phases during 
