On the structure of cross-striated muscle. 229 



If the manner in which the bright striae of the extended 

 living leg-muscles of insects are produced is rightly understood, viz: 

 that they are mainly caused by the effect which the local accumu- 

 lations of sarcoplasm (forming the transverse networks) produce upon 

 the light which is transmitted through the muscle, there will then be 

 no difficulty in understanding how it happens that the whole inter- 

 val between the dark striae of the contracted muscle has a bright 

 appearance. For with the approximation of these striae which is 

 attendant upon the bulging of the sarcous element and the concomitant 

 shortening of the muscle-segment, the optical effect produced by the 

 enlarging sarcoplasmic accumulations will involve more and more of 

 the segment and will eventually meet and blend with those of the 

 adjacent rows of sarcoplasmic accumulations; the bordering bright 

 striae encroaching more and more on the dim striae of the middle of 

 the resting segment and eventually obliterating the dim appearance 

 and substituting a continuous bright band, which occupies the middle 

 of the segment and embraces the whole interval between the dark 

 (sarcoplasmic) transverse bands which he opposite the junctions of the 

 muscle segments. 



The accessory disks of the leg-muscles. 



The accessory disks (Nebenscheiben), winch were described by 

 Flögel (Arch. f. mikr. Anat. VIII) and by Engelmann, are formed of 

 rows of discrete granules lying in the clear interval (isotropes Sub- 

 stanz) at either end of the row of sarcous elements which compose 

 the dim band (Querscheibe) of the muscle. They appear as dark dots 

 in the living fibre, are rendered very distinct by the action of dilute 

 acids, and have, in many alcohol preparations, the appearance of a 

 granular looking shading traversing the clear intervals. One can 

 scarcely avoid the belief that both these observers have had before 

 them the sarcoplasmic accumulations which are now known as the 

 transverse networks, but the existence of which had not at that time 

 been recognised. 



A doubt therefore would naturally arise whether the accessory 

 disks, which purport to be a distinct and separate part of each 



