On the structure of cross-striated muscle. 223 



of muscle, in which they are more decidedly stained than any other 

 part of the muscle substance, these may be said to represent all the 

 cross-striation which is visible, for the muscle-columns are dissolved 

 and nothing is seen except the lines representing - the inter-columnar 

 sarcoplasm. In fibres treated for a short time with dilute acetic 

 acid (vinegar) alone, the transverse membranes of Krause may also 

 be seen (Figs. 6 to 11). but the sarcous elements have here also 

 entirely disappeared. 



In the leg-muscles of most insects in the living condition, the 

 transverse networks, or at least the dots which, in the longitudinal 

 view of the fibres, are the optical expression of the filaments of those 

 networks, play a very conspicuous part in the production of the trans- 

 verse striation. For, in the first place they form in many muscular 

 fibres by their regular arrangement, series of double dotted lines which 

 are very distinct (Figs. 1, and 5 A). The effect of these upon the 

 light which is transmitted through the muscle has been already re- 

 ferred to (page 201 and note) and the arguments there adduced need not 

 here be recapitulated. Although Krause's membranes cannot usually 

 be distinguished in the fibres in which this appearance of rows of 

 dark dots with borderings of bright haloes is visible, their existence 

 can at any moment be shown by the action of dilute acid upon the 

 fibres: they are undoubtedly present, therefore, although obscured by 

 the effect which the transverse networks produce upon the light. In 

 the living fibre it is then by these transverse networks that the 

 characteristic narrow bright striae of the leg-muscles of insects are 

 mainly produced: the effect may, however, be aided by the light 

 reflexions which occur from the membranes of Krause. 1 ) 



*) I have already dealt, (p. 187) with the deep focus appearance which 

 shows (Fig. 5 C) the stria of Amici or Dobie's line in the middle of the bright 

 stripe and have given reasons for regarding this line, distinct as it may seem, as 

 not representing the true appearance of the fibre. It is needless, therefore, to say 

 thar I do not share with many other authors, including, I believe, Professor Krause 

 himself, the opinion that the stria of Amici is the optical expression of Krause's 

 membrane. A simple experiment will suffice to show that this is not really the 

 case. Let a fibre be chosen which exhibits, as in Fig. 5 of this article, or in 

 Fig. 15 in Kollett's memoir (Wiener Denkschriften Bd. 49) the stria of Amici when 

 the microscope is focussed deeply into the fibre, and the double rows of dots (which 



