MUSCULAR TISSUE 



[CH. VI. 



at Hensen's line. In the contracted muscle the clear part of the 

 muscle substance passes into these pores, disappears from view to a 

 great 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 sarco- 

 mere, 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 amoeboid, 

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



- S.E. 



K 



nmm 

 uffltf? 



S.E. 



FIG. 108. Sarcostyles from the wing-muscles 

 of a wasp. 



A, A'. Sarcostyles showing degrees of con- 



traction. 



B. A sarcostyle extended with the sarcous 



elements separated into two parts. 

 . Sarcostyles moderately extended (semidia- 

 grammatic). (E. A. Schafer.) 



FIG. 109. Diagram of a sarcomere 

 in a moderately extended con- 

 dition, A, and in a contracted 

 condition, B. 



K, K, Krause's membranes ; H, 

 plane of Hensen ; S.E., 

 poriferous sarcous ele- 

 ment. (B. A. Schafer.) 



protoplasm composed of two materials, spongioplasm and hyaloplasm. 

 In amoeboid movement the irregular arrangement of the spongioplasm 

 allows the hyaloplasm to flow in and out of it in any direction. In 

 ciliary movement the flow is limited by the arrangement of the 

 spongioplasm to one direction ; hence the limitation of the movement 

 in one direction (see p. 30). In muscle, also, the definite arrangement 

 of the spongioplasm (represented by the sarcous element) in a longi- 

 tudinal direction limits the movement of the hyaloplasm (represented 

 by the clear substance of the light stripe), so that it must flow either 

 in or out in that particular direction. The muscular fibre is made up 

 of Sarcostyles and the sarcostyle of sarcomeres. The contraction of 



* 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 diffusion through 

 its membrane. 



