1110 



GENERAL ANATOMY OR HISTOLOGY. 



and in which the appearances seen under the microscrope have been more differ- 

 ently interpreted, than the minute anatomy of muscular fibre. Schafer has 

 recently worked out this subject, particularly in the wing-muscles of insects, 

 which are peculiarly adapted for this purpose on account of the large amount of 

 interstitial sarcoplasm which separates the sarcostyles. In the following descrip- 

 tion we shall closely follow that given by Professor Schafer (Fig. 642). 



Each sarcostyle may be said to be made up of successive portions, each of 

 which Schafer terms a sarcomere. This is the portion, situated between two 

 membranes of Krause, which transversely divides the light band. Each sarcomere 

 consists of a central dark part, which forms a portion of the dark band of the 

 whole fibre, and is named by Schafer a sarcous dement. 1 This sarcous element 

 really consists of two parts, superimposed one on the top of the other, and when the 

 fibre is stretched, these two parts become separated from each other at the line of 

 Hensen (Fig. 642, A). On either side of this central dark portion is a clear layer, 

 most visible when the fibre is extended ; this is situated between the dark centre 

 and the membrane of Krause, and when the sarcomeres are joined together to 

 form the sarcostyle, constitutes the light band of the striated muscular fibre. 



When the sarcostyle is extended, the clear intervals are well marked and 

 plainly to be seen; when, on the other hand, the sarcostyle is contracted, 

 that is to say, the muscle is in a state of contraction, these clear portions 

 are very small or they may have disappeared altogether (Fig. 642, B). When the 



S.E. 



' 



111 



m 



FIG. 642. Diagram of a sarcomere. (After Schafer.) A. In moderately extended condition. B. In a con 

 sted condition. K.K. Membranes of Krause ; H. Line or plane of Hensen ; S.E. Poriferous sarcous element. 



tracted co 



sarcostyle is stretched to its full extent, not only is the clear portion very well 

 marked, but the dark portion the sarcous element will be seen to be separated 

 into its two constituents along the line of Hensen. 



The sarcous element does not lie free in the sarcomere, for when the sarcostyle 

 is stretched, so as to render the clear portion visible, very fine lines, which are 

 probably septa, may be seen running through it from the sarcous element to the 

 membrane of Krause. 



Schafer explains these phenomena in the following way. He considers that 

 each sarcous element is made up of a number of longitudinal channels, which 

 open into the clear part toward the membrane of Krause, but are closed at the line 

 of Hensen. When the muscular fibre is contracted the clear part of the muscular 

 substance finds its way into these channels or tubes, and is therefore hidden from 

 sight, but at the same time it swells up the sarcous element and widens and 

 shortens the sarcomere. When, on the other hand, the fibre is extended, this 

 clear substance finds its way out of the tubes and collects between the sarcous 

 element and the membrane of Krause, and gives the appearance of the light part 

 between these two structures ; by this means it elongates and narrows the 

 sarcomere. 



If this view is true, it is a matter of great interest, and, as Schafer has 

 shown, harmonizes the contraction of muscle with the amoeboid action of proto- 

 1 This must not be confused with the " sarcous element of Bowman." (See above. ) 



