475 



of the relations of anisotropous and isotropous substances to one an- 

 other within the fibrils, and the relative amount and arrangement of 

 fibrils and sarcoplasm or interfibrillar substance with respect to one an- 

 other: no light having been thrown upon the internal structure of the 

 substances — isotropous and anisotropous — which unite serially to form 

 the fibrils. 



A few authors, but none very recently, have selected the wing- 

 muscles of insects as a special subject of research ; amongst them, W. 

 Krause^), F. Merkel 2) and L. Ranvier^). But with the exception 

 of Krause, who described fine longitudinal lines within the anisotropous 

 substance, none appear to have noticed the actual structure of the 

 serial parts of the fibrils of these muscles, although from the fact 

 that they are easy of isolation and of much larger diameter than the 

 fibrils of ordinary muscle, their structure is not difficult of demon- 

 stration. This I showed in 1891 ■^), by means both of photographs 

 and drawings made from specimens prepared by the modified gold 

 method described by Rollett. In such specimens the minute structure 

 of the wing-fibrils comes out sometimes with remarkable distinctness, 

 for the anisotropous substance is deeply stained by the reagent, and 

 all the serial parts of these fibrils, viz: the lines of Dobie or mem- 

 branes of Krause (disques minces, Ranvier), the isotropous sub- 

 stance on either side of those membranes, and the lines of Hensen 

 bisecting the sarcous elements or principal disks, are all clearly visible 

 in the resting state of the fibril. Figure 1 shows the appearances 

 presented by a fibril in this condition. It has been drawn under a 

 Zeiss 2 mm apochromatic oil-immersiou, with extreme care and fidelity 

 to nature. Each principal disk (sarcous element) which is the only 

 part stained by the reagent, is separated in the middle into two halves, 

 and the line of Hensen is seen to be the optical expression of the 

 plane of separation. Each half shows longitudinal striations, but these 

 striations are not due, as was supposed by Krause, to the existence 

 of fine filaments in the principal disk, but to longitudinal pores, which 

 are very obvious in the isolated sarcous elements depicted in Figure 2. 



In the communications already referred to I have brought forward 

 evidence that the process of contraction of the fibril is accompanied 

 by a transference of (fluid ?) isotropous substance into the anisotropous 



1) Handbuch, 1876. 



2) Arch. f. mikrosk. Anat., Bd. 8, 1872; Bd. 9, 1873; Bd. 19, 1881. 



3) Traite technique. 



4) Proc. Roy. Soc, Vol. 49, p. 280. Intern. Monatsschr. f. Anat. u. 

 Physiol., Bd. 8, p. 178. 



