HISTOGENESIS AND STRUCTURE 



109 



when the sarcoplasm, with its interstitial granules, is relatively abundant, 

 : dark/ In the latter fibers many of the nuclei may be centrally located. 



FIG. 122. FIBRILS FROM THE WING 

 MUSCLES OF A WASP. 



A, compressed; B, stretched; C, un- 

 contracted. The alternate dark and 

 light disks are prominent; the mem- 

 brane of Krause in the light disk, and 

 the line of Hensen in the dark disk are 

 well shown. Very highly magnified. 

 (After Schafer.) 



FIG. 123. LONGI- 

 TUDINAL SECTION 

 OF A PORTION OF 

 A STRIPED MUS- 

 CLE TRABECULA 

 OF LIMULUS, 

 SHOWING A NU- 

 CLEUS OF SER- 

 RATED CONTOUR 

 WITH THE TELO- 

 PHRAGMATA AT- 

 TACHED TO THE 

 SERRATIONS. 



The nucleus lies 

 in an undifferenti- 

 ated mass of sarco- 

 plasm containing 

 below a deutoplas- 

 mic granule. The 

 adjacent myofibrils 

 simulate a cell mem- 

 brane. Fleming's 

 fluid, iron-hematox- 

 ylin. X 2000. 



Most mammalian muscles contain both types of fibers, but with the 

 'light' greatly in excess. When a muscle consists chiefly of 'light' fibers 

 it is a 'white' muscle; when the 'dark' fibers are abundant it may be 



