60 



CELL, DIFFERENTIATION AND THE ELEMENTARY TISSUES 



striation of the whole fiber. Under certain treatment the sarcostyles break 



transversely into smaller discs by cleavage at the line of Krause's membrane. 



The sarcostyle is, therefore, composed of a number of smaller elements 



joined end to end. These are the sarcous elements of Bowman. The sar- 



FIG. 74. Diagram of Segment of Muscle Fiber, showing Sarcostyle A, Sarcous element B. 

 Krause's line C, Hensen's line D. 



cous element has a highly refractive denser middle piece surrounded by a 

 less refractive more fluid material. The polarizing microscope reveals the 

 fact that the middle piece which corresponds in position to the dark trans- 



FIG. 75. 



FIG. 76. 



S'.Ei 



S.E.. 



FIG. 75. Sarcostyles from the Wing-Muscles of a Wasp. A, A', Sarcostyles showing degrees 

 of retraction; B, a sarcostyle extended with the sarcous elements separated into two parts, C, 

 sarcostyles moderately extended (semidiagrammatic). (E. A. Schafer.) 



FIG. 76. Diagram of a Sarcomere in a Moderately Extended Condition, B. K, K, Krause's 

 membranes; H, plane of Henson; 5, E, poriferous sarcous element. (E. A. Schafer.) 



verse band is doubly refractive, isotropic, while the surrounding material, 

 the light band, is singly refractive, anisotropic. 



