On the structure of cross-striated muscle. 217 



Before, however, doing this it will be as well again to point out 

 what are the reasons for applying the same term, viz: mnscle-colnmns 

 or sarcostyles, to these longitudinal elements of the ordinary muscles and 

 to the separable longitudinal elements of the wing-muscles. 



Those reasons are briefly as follows: — In each case they are 

 the separable longitudinal elements of the muscle-fibre: this is, in fact, 

 a bundle of these elements, which are enclosed in both cases by a 

 sarcolemma and are separated from one another by a greater or less 

 amount of „sarcoplasm". In each case also these muscle-columns or 

 sarcostyles are composed of a number of segments separated from one 

 another by transverse membranes, and each segment is composed of 

 a sarcous element in the middle of the segment and a clear interval 

 of variable size lying between the sarcous element and the transverse 

 membrane. The correspondence therefore, in general structure is close, 

 and the similarity of their behaviour to various reagents and methods 

 of staining proves them to possess in each of their constituent parts 

 essentially the same chemical constitution. There can therefore be 

 very little doubt that they are both morphologically and physiolog- 

 ically equivalent to one another, and it is probable that there will 

 exist a close similarity even in minute details of their structure. If 

 therefore the wing-sarcostyles can be shown not to be fibrillated, it 

 behoves us to examine very closely into the question of the reputed 

 fibrillation of the sarcostyles of ordinary muscle. 



It is not improbable that to most readers the fact that an ordi- 

 nary muscle, such as the leg-muscle of an insect, can be readily split 

 up into ..fibrils'' after it has been hardened in alcohol, is too obvious to 

 be questioned. It is nevertheless a fair object of inquiry whether the 

 longitudinal elements which are obtainable from alcohol and osmic 

 preparations (Fias. 22. 23) really represent fibrils or whether they 

 merely represent sarcostyles. Prom the result of my own observations 

 upon tliis point, which have been made with the special view of de- 

 ciding it. 1 believe that tlieso so-called fibrils, even the smallest, are 

 invariably muscle-columns. Jb'or it is to be remembered that the sar- 

 ■:< styles are themselves of a. very small diameter, especially in the 

 extended muscle, and that this diameter is still further diminished by 



