ORGANISATION AND STRUCTURE OF MUSCLE 



41 



transverse bands or stripes to which these give rise in the 

 entire fibre, by a system of letters. The large sections (Q), which 

 appear dark on lowering the objective, are divided by the band 

 (7i), which is light with the same focus, of varying breadth, and 

 not usually well defined, into three parts the two " dark 

 bands " (Qu&rschichten), and the less strongly refractive Hensen's 

 stripe (" Hensenche " Mittelscheibe, h), which is not always visible. 

 Schiefferdecker gives the name of " middle band " (M. " Mittel- 

 schicht ") to a very fine dark line, first accurately described by 

 Hensen, which sometimes appears in the " middle stripe " (h), 

 but is not always visible. The segments (Q) are generally longer 



FIG. 27. Schema of the transverse striation of Beetle-muscle. (Rollett.) 



in Arthropod muscles than in Vertebrates, so that, with the 

 coincident longitudinal striation, the muscle-fibres look as if they 

 were composed of long, dark rows of granules (Fig. 31). The 

 dark band which bisects the clear segment with a low objective 

 (as described by Amici) is known as Dobie's line (Z. Zwischen- 

 schicht, Engelmann's " Zwischenscheibe "). Krause described this 

 band as the " transverse line " and " basal membrane " of his 

 " muscle-cases " (infra). Between (Z) and the two clear segments 

 (J), which in the simplest case (Fig. 27, /) are only sepa- 

 rated by it, two dark bands are occasionally visible ; they are 

 very inconstant in their appearance, and are denoted by Eollett 



