MUSCULAR TISSUE. 



[CH. VI. 



sarcous element is really double, and in the stretched fibre 

 (fig. 1 08, B) separates into two at the line of Hensen. At either 

 end of the sarcous element is a clear interval separating it from 

 Krause's membrane ; this clear interval is more evident in the 

 extended sarcomere (fig. 108, B), but diminishes on contraction 

 (fig. 1 08, A). The cause of this is to be found in the structure of 

 the sarcous element. It is pervaded with longitudinal canals or 

 pores open towards Krause's membrane, but closed at Hensen's 

 line. In the contracted muscle the clear part of the muscle sub- 

 stance passes into these pores, disappears from view to a great 



Fig. 108. Sarcostyles from the wing-muscles 

 of a wasp. 



A, A'. Sarcostyles showing degrees of con- 

 traction, 

 u. A sarcostyle extended with the sarcous 



elements separated into two parts. 

 c. Sarcostyles moderately extended (semidia- 



grammatic,). (E. A. Schafer.) 



- S.E. 



- S.E. 



Fig. 109 Diagram of a sarcomere 

 in a moderately extended 

 condition, A, and in a con- 

 tracted condition, B. 



K, K, Krause's membranes ; H, 

 plane of Hensen ; S.K., 

 poriferous sarcous ele- 

 ment. (E. A. Schafer.) 



extent, swells up the sarcous element, widens it and shortens the 

 sarcomere. In the extended muscle, on the other hand, the clear 

 substance passes out from the pores of the sarcous element, and 

 lies between it and the membrane of Krause ; this lengthens and 

 narrows the sarcomere.* This is shown in the diagrams. It 

 may be added that the sarcous element does not lie free in the 

 middle of the sarcomere, but is attached at the sides to a fine 

 enclosing envelope, and at either end to Krause's membrane by 

 fine lines running through the clear substance (fig. 109, A). 



This view is interesting, because it brings into harmony amoe- 

 boid, ciliary, and muscular movement. In all three instances we 



* The existence of open pores is not admitted by all observers. These 

 regard the passage of fluid in and out of the sarcous element as due to diffu- 

 sion through its membrane. 



