220 E. A. Schäfer, 



The cross-striation of the wing-columns is then due to their being 

 composed of alternating - substances of different chemical nature. Of 

 these the one (sarcous element) which occupies the middle of each 

 segment is chromatic and probably more solid: it stains deeply with 

 haematoxylin or with gold after alcohol, and is much more highly 

 refracting than the other, winch is as clear as water, varies greatly 

 in amount and shows no trace of further transverse striping. The 

 sarcous element, on the other hand, may exhibit distinct bands. I 

 have already endeavoured to explain the mode in which the substance 

 of the sarcous element may, under the influence of an extending force, 

 break up into a series of such bands. 



In the unextended (contracted, retracted) sarcostyles of the wing- 

 muscles such multiple bands are not seen, and the sarcous elements 

 or chromatic disks so closely approach the membranes of Krause as 

 to render the clear intervals very short and the membranes of Krause 

 difficult or impossible of observation. 



In separated muscle-columns of the living wing-muscle, a greater 

 or less degree of retraction is the most common condition observed. 

 In the living state the difference of refrangibility between the sarcous 

 element and the substance of the clear interval is far less marked than in 

 the hardened muscle, and it is difficult to see the line of junction 

 between them. This difficulty is increased by the effect which the 

 membranes of Krause produce upon the light transmitted through the 

 muscle, causing, probably by reflexion from their surfaces, that part 

 of the muscle substance which is immediately adjacent to them, to 

 appear much brighter than the rest. This effect has been already 

 referred to (see p. 209) as obscuring the line of junction between the 

 sarcous element and the clear interval, except in greatly extended 

 fibres. By virtue of this effect of the Krause membrane, the fresh 

 fibre shows alternating dim bands and bright bands, the dim band 

 occupying the middle of each segment, the bright bands intervening 

 between them and bisected by the membrane of Krause. The bricht 

 effect is here, however, certainly enhanced by the optical conditions 

 of the muscle and although corresponding approximately in situation to 

 the clear interval of the alcohol muscle, is somewhat differently produced. 



