CH. VI.] 



VOLUNTAKY MUSCLE 



67 



remarkable for perfection of mechanism have consequently been 

 the subject of many researches. In the wing muscles of these 

 animals the sarcostyles are separated by a considerable quantity of 

 interstitial sarcoplasm, which may be of nutritive importance; at 

 any rate it allows the intimate structure of the individual sarcostyles 

 to be worked out very thoroughly. As the result of such work, 

 Schiifer has arrived at the following conclusions : 



Each sarcostyle is subdivided in the middle of each light stripe by 

 transverse lines (membranes of Krause) into successive portions, 

 which may be termed sar comer es. Each sarcomere is occupied by a 

 portion of the dark stripe of the whole fibre; this portion of the 

 dark stripe may be called a sarcous element* The sarcous element 



K -, 



S.B. 



B 



S.K. 



FIG. 81. Sarcostyles from the wing-muscles 



of a wasp. 



A, A', Sarcostyles showing degrees of con- 

 traction. 

 11, A sarcostyle extended with the sarcous 



elements separated into two parts, 

 c, Sarcostyles moderately extended (semidia- 

 grammatic). (E. A. Schiifer.) 



FIG. 82. Diagram of a sarcomere 

 in a moderately extended con- 

 dition, A, and in a contracted 

 condition, B. 



K, K, Krause's membranes ; ji, 

 plane of Hensen ; S.E., 

 poriferous sarcous ele- 

 ment. (E. A. Scliiifer.) 



is really double, and in the stretched fibre (fig. 81, 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. 81, B), and 

 diminishes on contraction (fig. 81, A). The cause of this is to be found 

 in the structure of the sarcous element. It is pervaded with longi- 

 tudinal canals or pores open towards Krause's membrane, but closed 

 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 



f Notice that this expression has a different meaning from what it originally 

 had when used by Bowman. 



