On the structure of cross-striated muscle. 191 



bright striae. These I shall term Krauses membranes, intersegmental 

 membranes, or simply transverse membranes. By these the sarcostyle 

 is divided up into segments (sarcomeres). In the fresh muscle each 

 segment shows a broad dim band, occupying the middle of the 

 segment and narrower bright bands lying next to the intersegmental 

 membrane. The dim band may have a lighter or darker streak passing 

 across its middle; this is Sensen' s stria. Alcohol -preparations of 

 muscle show the segment to be composed of a solid-looking mass of 

 sarcous substance which stains deeply with haematoxjdin and other dyes, 

 and of a clear substance which remains unstained. For the former, 

 which corresponds generally to the dim band of the living muscle, 

 the name sarcous element may conveniently be retained, since there 

 is little doubt that it was these elements, forming by their linear con- 

 catenation the sarcostyles (the so-called „fibrils"), that were seen and 

 described by Bowman under that name in 1840. The substance of 

 the sarcous elements (chromatic substance, sarcous substance, anisotro- 

 pous substance of authors) can be shown, at least in the wing-muscles, 

 to be pierced by fine longitudinal tubules: the longitudinal striation 

 which these tubules produce has usually, but erroneously, been taken 

 to indicate that the sarcostyles are composed of fibrils. *) 



At either end of the sarcous element and separating it from the 

 inter -segmental membrane is an interval, occupied by a substance 

 which remains completely unstained by reagents which give a deep colo- 

 ration to the sarcous elements. It may be termed the clear substance 

 or hyaline substance of the segment. It is very variable in amount 

 relatively to the sarcous element, being sometimes present in so small 

 a quantity that the sarcous elements are almost in contact with the 

 intersegmental membranes, at other times occupying as much space in 

 the segment as the sarcous element itself. It appears more exten- 

 sive with the stretching of the fibre. It is opposite this clear part 

 of the segment that in the ordinary or leg-muscles the transverse-net- 



*) As already mentioned, the term „fibril" has been frequently applied to 

 the muscle-columns or sarcostyles themselves and specially to those of the wing- 

 muscles („wing-fibrils"). It will be best therefore to discard the use of the term 

 altogether. 



