HISTOGENESIS AND STRUCTURE 



101 



ger-Seidel) ; this interpretation has recently been again supported by 

 Zimmermanii. This interpretation would mean that from a syncytium a 

 cellular tissue has secondarily arisen by the appearance of cement, lines, 

 secondary cells having been formed in a syncytium, irrespective of the 

 original genetic units. A number of facts render this interpretation inad- 

 missible, chief among which are their occasional supernuclear position, and 

 their peripheral location. A more recent interpretation conceives of them 

 as places where the muscle fiber grows, that is, as sarcomeres in the mak- 

 ing (Heidenhain). Among the countervailing facts to such interpretation 

 are chiefly the absence of transition stages, their relative scarcity at the 

 period of greatest growth of the heart, and their continued abundance in 

 full-grown, even aged, hearts. The suggestion has occasionally been made 

 that they are somehow related to a phase of contraction. This seems the 



J 2 



Q 



I 



C I 



Id 



I J 



Telophragmo. 

 J granule 



Q-granule 



Mesophragma 

 Q-granule 



J granule 

 J-gra n ule 



Transverse 

 fiber net- 

 work 



Transverse 

 fiber net- 

 work 



FIG. 110. -- DIAGRAM OF A 

 STRIPED MUSCLE FIBER, AC- 

 CORDING TO HEIDENHAIN. 



The transverse fiber network 

 may be a trophospongium. 



FIG. 111. --SIX- 

 LOB E D NUCLEUS 

 FROM THE HEART 

 MUSCLE OF LIM- 

 u L u s , SHOWING 

 THE CONTINUIT\ 

 OF THE NUCLEAR 

 WALL WITH THE 

 TELOPHRAGMATA. 



X 1300. 



more likely interpretation. Since the discs are largely permanent when 

 once formed, and undergo subsequent modification, they must represent an 

 irreversible condition of the contraction phase. The interpretation of the 

 disks as irrecersiUr contraction Itaiiclx rests largely upon the similarity be- 

 tween the simplest types and the 'contraction bands 1 <if Rollet. both char- 

 acterized by accumulation of dark staining granules about the Z membrane. 

 In the older hearts, where they are mechanically modified, and in diseased 

 hearts, as in hypertrophies, where probably a chemical modification is also 

 8 



