Muscle- Columns which form the Winy-Muscles of Insects. 281 



through it (Haycraft) ; moreover, many of the sarcostyles show no 

 such varicosities. A more valuable, because more sharply selective, 

 method of staining is that recommended by Bollett (' Wien. Akad. 

 Denkschr.,' vol. 51) for alcohol-glycerine muscles. This consists 

 simply in the after- application of the gold-formic method to 

 the tissue. In place of treating the fresh muscle with, chloride 

 of gold and afterwards with formic acid, the alcohol muscle, 

 which has been afterwards steeped in glycerine, is taken. If 

 fresh muscles are thus treated, the sarcoplasm alone is stained, the 

 earcostyles remaining colourless (or they may be entirely dissolved by 

 the action of the formic acid). In this way, in the leg-muscles, the 

 of ten- described appearance of a network is obtained. But if the 

 alcohol- glycerine muscle be taken, the reduction of the metal takes 

 place in the sarcostyles, and almost exclusively in their dark bands, so 

 that, while the interstitial sarcoplasm and the clear bands of the 

 sarcostyles remain clear and colourless, the dark bands of the sarcc- 

 styles are deeply coloured of a tint varying from an intense purple- 

 red to a faint purple-blue. Rollett recommends the application of 

 this method to the study of the structure of the leg-muscles, but it is 

 still better applicable to that of the wing-muscles, since it brings out 

 in them, with a clearness which renders the application of the photo- 

 graphic method comparatively easy, points of structure which, up to 

 the present, with the usual methods of investigation, have remained 

 3ure. 



Jefore describing the special points which are thus capable of 

 elucidation, it is necessary to adopt names for the several parts of the 

 sarcostyle. For the more or less cylindrical disk which forms the 

 dark band I shall retain the name " sarcous element," without 

 thereby intending to imply that it accurately corresponds to the part 

 to which that name was originally applied by Bowman ; in a general 

 sense, I believe that it will be found to do so. The term represents, 

 on the whole, the Querscheibe of the German, the disque epais . of 

 French, authors. The fine line which bisects the light band I shall 

 term "transverse membrane" (Quermembran, Krause ; Zwischen- 

 schcibe of German authors; disque mince of French writers). The 

 light space separating the ends of the sarcous elements from the 

 transverse membranes may, for the present, be simply spoken of as 

 the "clear interval;" it corresponds with the isotropons substance 

 of authors. The segment of a sarcostyle comprised between two 

 transverse membranes may be termed " muscle-segment " or " sarco- 

 mere " (Muskelkdstchen, Krause). 



The relative amount of the sarcomere occupied by its several parts 

 varies with the degree of extension or retraction (? contraction) of 

 the tissue. In the retracted condition (figs. 1 and la) the sarcostylp, 

 which is relatively thick and moniliform, appears formed almost 



u 2 



