580 H. p. KJERSCHOW AGERSBORU 



sind Biindel von Myofibrillen ohne innere Sarcaxe. Der 

 langliche Kern liegt der Faser dicht angepresst.' Continuing 

 on the same subject, but dealing with a different type, i.e. 

 Helix pomatia, he says : ' Die Fasern sind von rimdlichem 

 Querschnitt, langgestreckt, glattfibrillar mid zeigen den 

 Kern seitlich in einem geringen Sarcrest (Zellkorper) anliegen.' 

 His comment on the muscles of Anodonta muta bills 

 is much the same as for those already cited, i.e. : ' Die glatten 

 Muskelfasern zeigen gewohnlich nichts Auffallendes. Jede 

 Faser besteht aus parallel verlaufenden Fibrillen. Der lang- 

 liche Kern liegt der Faser einseitig an, innerhalb einer geringen 

 Sarcmenge die als Zellkorper zu bezeichnen ist.' 



Schneider's description of molluscan muscle is rather general- 

 ized and, in fact, fails to bring out the facts concerning the 

 finer structure. The muscle-bundles of M. leonina are 

 surrounded by a thin membranous sheath, the perimysium 

 (PI. 31, fig. 33, Ms), and each individual muscle-cell by an 

 exceedingly thin membrane, the endomysium (Mt). Between 

 the muscle-fibres, or muscle-cells, are primitive connective-tissue 

 cells (Inct). The muscle-cell or -fibre (PI. 31 , fig. 33, PI. 37, fig. 8'2,) 

 is differentiated into two sarcoplasmic regions : an outer finely 

 granular and an inner coarsely granular region with a trans- 

 parent ground substance. At the periphery of each region, 

 very coarse granules are arranged in such a way so as to 

 give the appearance of a granular network enclosing each 

 (figs. 33, Sar, 82, MijJ). The outer of these may be in close 

 relation with the sarcolemma if such a one is present ; the 

 inner granular network holds a similar relation to the finely 

 granular region as the outer granular network holds to the peri- 

 phery of the cell, each enclosing, as it were, two different 

 cytoplasmic regions of the cell. There are thus four kinds of 

 granules in the muscle-cell relative to their location and size. 

 These granules may be designated as myofibrillae because of 

 their linear arrangement. The nucleus is placed centrally 

 within the ground substance of the inner region surromided by 

 the coarser myofibrillae, immediately, and ultimately by the 

 outer and more finely granular substance. In staining capacity, 



