28 H. E. JORDAN 
contraction as does insect leg muscle. Evidence will be pre- 
sented for the conclusions that all varieties of striped muscle 
behave during contraction in an essentially identical manner; 
that the contraction band of a contracting fiber is a genuine 
structural entity, not an optical illusion, representing an actual 
reversal of striae with respect of the deeply staining constituent 
of the stratified sarcoplasm; and that this contraction band 
(disc) is the primordium of the several types of intercalated discs 
of cardiac and skeletal muscle. Incidentally must be considered 
also the nature and significance of the sarcomeres, of the ino- 
phragmata (telophragma and mesophragma), of the accessory 
disc (of Merkel and Rollet), and of the distribution of the alleged 
anisotropic materials. 
V. DESCRIPTION 
a. Leg muscle 
The condition of the relaxed muscle fiber is illustrated in 
figure 14. This fiber was fixed in 95 per cent alcohol and stained 
with iron-hematoxylin. The unstained fiber has an essentially 
identical appearance. The deeply staining portions of the 
stained fiber simply appear more faint in unstained specimens. 
The fiber is slightly distorted below. The sarcolemma, on the 
left, is slightly festooned, due to the unequal contracting action 
of the fixing fluid upon the muscle fibrils and the sarcolemma. 
Since the fibrils shorten more than the sarcolemma under this 
influence, and since the sarcolemma is intimately connected with 
the telophragmata, the sarcolemma accommodates itself to the 
shortened condition of the fibrils by separating from the fiber 
in the form of arcades. Q and J are of about equal thickness. 
The telophragma appears relatively robust, somewhat granular 
and deeply staining. The granular appearance of the telo- 
phragma is due to swellings at the points where the myofibrils 
are attached to it. An accessory (N) dise is very conspicuous. 
It is formed by the horizontal alignment of modified minute areas 
of the myofibrils in the vicinity of the telophragmata. It has 
apparently much the same chemical constitution as the Q discs. 
