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H. E. JORDAN AND K. B. STEELE 



higher to a lower level of focus, when one disc fades out of view 

 as the other passes in, no differentiated connecting substance 

 ('riser') appears, as one would expect if these two discs repre- 

 sented portions of an irregular cement line cut tangentially, as 

 interpreted by Zimmermann and his students. 



The most plausible interpretation, it would seem, must regard 

 the dark-staining granules or rodlets of the ' discs' as local modi- 

 fications or contractions at anisotropic levels of the myofibrillar 



J 



r 



Fig. 3 Branching fiber of monkey heart with four plate-like discs, showing 

 their relation to the dark bands. 



Fig. 4 Short portion of fiber of monkey heart showing super-nuclear position 

 of three discs. 



Fig. 5 Two granular discs of monkey heart at different levels of focus. In 

 passing from the higher to the lower level of focus no connecting membrane or 

 'riser' appears. 



Fig. 6 A two-step, comb-like, disc of monkey heart, in longitudinal width equal 

 to that of the isotropic and two anisotropic discs. The two portions are connected 

 by a coarse deep-staining membrane. The 'teeth' of the 'comb' are interpreted 

 as locally contracted portions of adjacent fibrillae. 



Fig. 6 shows a rare variation. Here the disc may extend the 

 longitudinal distance of half or even an entire lighter band. In 

 form it has a 'comb' structure. When at different levels, as here, 

 the several sections are connected by a robust deeply-staining 

 membrane. The appearance simulates protoplasmic processes or 

 'intercellular bridges.' However, if this were a correct interpre- 

 tation, they would undoubtedly be very much more numerous. 



