232 E. A. Schäfer, 



each pair of sarcoplasmic accumulations. This also appears sometimes 

 to have been regarded as representing an accessory disk. 1 ) 



It is not surprising therefore to find that there is very little 

 agreement amongst different authors as to the appearance, position 

 and optical and staining properties of the so-called accessory disks. 

 Upon one point, however, all observers seem to be agreed: that they 

 are by no means a constant or necessary element in the structure of 

 muscle. For myself, I have never obtained satisfactory evidence of 

 their existence as separate elements of the muscle-segment of the leg- 

 muscles. I am not prepared at present to deny that they are ever 

 present, for it is quite possible to suppose that the sarcous elements 

 may here, as well as in the wing-muscles, be liable to undergo a 

 segmentation when much extended. I would merely raise a note of 

 warning to future observers not to accept the appearance of a dotted 

 line in the clear interval as evidence of such an accessory disk, but 

 to determine whether this appearance may not be due to some other 

 cause, and especially to investigate the behaviour of its component 

 dots to the action of dilute acid. If, as has been the case in those 

 cases which I have myself investigated, the dots resist the action of 

 the acid, which swells and dissolves the substance of the muscle- 

 segments, their sarcoplasmic nature may be taken as proved.' 2 ) 



*) This is the case with the accessory disks (N) in Fig. 19 &, of Rollett's 

 second communication, the parts thus marked being in no other way distinguished 

 from the substance of the clear interval of which they form a part. On the other 

 hand, in Rollett's Figs. 10, 22. 23, the dots marked IS" certainly represent sarco- 

 plasmic enlargements, and the same is also the case with those shown in Fig. 13 

 which with further action of acid assume the highly characteristic appearance of 

 the sarcoplasmic dots shown in Fig. 17. This is probably also true for several of 

 the other disks shown in Eollett's figures, in spite of the fact that they are 

 represented as being in a directly continuous line Avith the sarcous elements 

 of Q. In uttering this opinion I do not imply that the figures are purposely 

 modified to show this continuity, for the difficulty of determining the point is 

 very great. 



-) It may justly be alleged by Rollett that this is precisely the test which 

 in certain cases he actually adopted; with the result that the dots shown so 

 clearly in Figs. 11 h of his first communication underwent a subsequent swelling 

 from the further action of the acid and became replaced by clear polygonal areas 

 bounded by a network of fine lines with enlargements at the nodes of the network. 

 To me, however, it seems that the clear areas are quite differently produced. I con- 



