ORGANISATION AND STRUCTURE OF MUSCLE 



49 



It is also easy to see that the dark, sharply defined 

 bands appear where the relaxed muscle presents the segments, 

 (JZJ), or (JNE,Z,E N J), and that the light bands correspond 

 essentially with the contracted striae (Q li Q). 



The muscle-fibres of insects, killed by strong alcohol, often 

 exhibit local contractions (" fixed waves of contraction ") in which- 

 the histological changes pro- 

 duced in the striated fibrils 

 during the transition from rest 

 to contraction can be ascer- 

 tained exactly by means of 

 staining methods and reagents. 

 These very subtle manifestations 

 are of the greatest theoretical 

 interest, and must be discussed 

 a little more fully. 



As before, we may accept 

 the penetrating conclusions of 

 Rollett (22). On examining a 

 well-fixed wave of contraction, 

 from a fibre of Otiorhyncluis 

 mastix stained with hsematoxy- 

 lin (Fig. 31), it is in the first 

 place evident that the dark-blue 

 band (C).of the contracted por- 

 tion of the fibre, Basse's " con- 

 traction-disc," is derived from 

 the transformation of the system 

 (JNE,Z,ENJ), and is there- 

 fore the same section which 

 Engelmann denotes as isotropous, 

 and Eollett as the arimetabolous 

 layer (a). 



In the relaxed arimetabolous layers the bands (Z) and (N) are 

 deeply stained, the bands (E) and (J) not at all, or very slightly ; 

 in the relaxed " metabolous " sections (Q h Q) (Engelmann's 

 " anisotropous " layer), which Eollett denotes by /^, the ends of 

 Q are more deeply stained than the centre h (Hensen's stripe). 

 With increasing contraction of the section (a), the diminishing 

 bands (N) draw nearer and nearer to (Z), until at last the two 



FJG. 31. Muscle- fibre of Otiorliynchus mastix, 

 showing wave of contraction. (Rollett.) 



bam 



