HISTOGENESIS AND STRUCTURE 



101 



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

 Zimmermann. 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 loca- 

 tion. A more recent interpretation conceives of 

 them as places where the muscle fiber grows, that 

 is, as sarcomeres in the making (Heidenhain). 

 Among the countervailing facts to such interpre- 

 tation are chiefly the absence of transition stages, 

 their relative scarcity at the period of greatest 

 growth of the heart, and their continued abun- 



Telophr 



Q-granule 



Mesophragma 



Transverse 

 fiber net- 

 work 



FIG. 111. LONGI- 

 TUDINAL SECTION 

 OF PORTION OF 

 WING MUSCLE 

 FIBER OF MANTIS, 

 AT MID-PHASE OF 



CONTRACTION. 



z, telophragma; 

 h, Hensen's disk; 

 j, isotropic disk; 

 q, anisotropic disk; 

 q. s., g-sarcosome ; 

 j. s., j-sarcosome. 

 X1600. 



FIG. 110. DIAGRAM OF A 

 STRIPED MUSCLE FIBER, AC- 

 CORDING TO HEIDENHAIN. 

 The transverse fiber network 

 may be a trophospongium. 

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

 that they are related to a phase of contraction. This seems more likely. 

 Since, once formed, disks are largely permanent, and undergo subsequent 

 modification, they must represent an irreversible condition of the con- 

 traction phase. The interpretation of the disks as irreversible contrac- 

 tion bands rests upon the similarity of the simplest types and the con- 

 traction bands of Rollet, both characterized by accumulation of dark stain- 



