290 H. E. JORDAN AND J. B. BANKS 



deeply staining band in series with the telophragmata, com- 

 posed of modified bacillary segments of the included portions 

 of the involved peripheral myofibrils (fig. 1). The modification 

 shows itself chiefly in an enhanced tingibility in certain stains, 

 e.g., hemalum. The modification is apparently, fundamentally, 

 chiefly chemical. Such a disc is originally bisected by a telo- 

 phragma. In the case of certain of the simpler discs in which 

 the telophragma is not discernible, they appear to shade later- 

 ally into a telophragma or abut upon it at the lateral mid-point 

 (fig. 2). That the discs are peripheral structures for the most 

 part can be demonstrated by changing the level of focus, when 

 the disc either disappears from the field or can be traced in a 

 lateral or spiral direction to an underlying or overlying surface. 

 The same fact can be even better demonstrated in transverse 

 sections. In figure 7 is shown a simple disc involving only the 

 peripheral myofibrils of the radial lamellae in approximately a 

 quarter of the circumference. In figure 8 two discs appear, one 

 internal to the peripheral element. In both sections the discs 

 are at the same level as the nucleus. Figure 25 shows a scat- 

 tering of smaller discs throughout the fiber, probably the result 

 of a spiral twisting which caused an inturning of portions of 

 originally peripheral discs. 



In figure 1 are shown two successive discs in series with the 

 telophragmata. Their location and general structure agrees 

 with that of contraction bands. The upper two discs in figure 2 

 show the same structure and relationships. In figure 1 both 

 discs cover the entire breadth (transverse) of the fiber. Discs 

 may be of much lesser breadth, indeed including only a single 

 fibril ; but narrower discs may also in certain cases represent trans- 

 verse sections of broader discs, e.g., as in figure 9. Again, similar 

 discs of lesser width (longitudinal) occur. These represent the 

 original condition, both phylogenetically and ontogenetically 

 (Jordan and Steele (14) ), the wdder discs being a modification 

 resulting from a traction produced by the contracting myocar- 

 dium. That the discs are subjected to the modifying influence of 

 a traction is indicated also by the frequently constricted condi- 

 tion of the fiber in the region where the discs are located (fig. 1). 



