

Dwight.] 122 [Nov. 5, 



so near together that no other substance is visible between them, but 

 sometimes they are separated into two distinct lines in a transparent 

 ground substance, and again they may be so close together as to give 

 the band an almost homogeneous appearance. On each side of these 

 bands is a glaring white one, usually broader on one side than on the 

 other. As the stage is rotated the brighter band pales, and the dim- 

 mer one brightens, while minute changes in the adjustment or illu- 

 mination produce similar almost indescribable effects. 1 The bright 

 bands are connected by a broad gray stripe, which is midway be- 

 tween two black bands. I have never seen a lighter stripe in the 

 middle of the gray one in muscle inside the body, but can fully con- 

 firm the common account of it in fibres pulled from the leg of the fly. 

 To recapitulate; a fibre at rest consists of a series of gray stripes 

 with white borders situated between black granular bands. 



The second state is best studied on fibres running to the lower part ' 

 of the tendon that passes from the tibia to the end of the limb, for in 

 many positions of the leg they are completely relaxed, and hang in 

 graceful curves. When, as sometimes happens, the tendon is broken, 

 they are seen to particular advantage. The whole fibre is broader 

 than in the first state. The black bands are usually somewhat nar- 

 rowed, and also drawn nearer together. Their granular nature can 

 almost always be made out, but the granules are never seen in two 

 rows. The white and gray stripes are both visible, but are narrower, 

 especially the former, than in the normal condition. The edges of 

 the fibre are scalloped. The ends of each projection come into the 

 borders of the black bands, the greatest bulging being opposite to 

 the middle of the gray. 



In the third, or stretched condition, the fibre is decidedly narrower, 

 with a peculiarly sharply defined outline. The granular bands are 

 pulled apart into two parallel lines of dots lying in a brilliant clear 

 ground, which is continued into the two white bands. The gray 

 band is lighter, and the bright bands darker than when at rest, so 

 that all parts of the ground substance present nearly, though not 

 quite, the same appearance. 2 The appearances of contracted fibre 

 will be best described in connection with the accompanying phe- 

 nomena. 



On looking at the tibia or femur when the fibres are in active con- 

 traction, the attention is constantly distracted by the strangeness of 



1 Vide Heppner in Archiv fur Mikroskopiscke Anatomie, Band v, Heftl. 



2 In fig. 2, C, the difference between the gray and white is too marked. 



