440 
ME. E. A. SCHAFER ON THE MINUTE STRUCTURE OF 
appearance on each side of it is produced by a total reflection of the rays of light from 
its surfaces — considering, from the fact of its similar behaviour under crossed Nicols, 
the substance forming the clear stripe to be similar in nature to the rest of the muscle- 
substance, with the exception of the Zwischensubstanz before mentioned. As a further 
indication that the bright bands are due to such an optical effect as he described, FIeppner 
remarked that their position became altered according as the mirror was inclined or the 
stage rotated. 
Quite recently three important conti ibutions to the study of the structure of striped 
muscular fibre have appeared; those, namely, by Flogel*, Merkel-)*, and EngelmannJ 
respectively. Merkel, studying the fibres of the Arthropoda, principally by means of 
alcohol preparations, finds the transverse line of Krause to be not simple, as believed by 
the latter, but in reality to be made up of two lines representing juxtaposed membranes 
(terminal disks or Endsclieiben), best seen when the fibre is stretched. He further 
describes an exceedingly indistinct disk ( Mittelscheibe ) in the middle of the dim stripe of 
the muscle, not always visible, and often only represented by a somewhat lighter appear- 
ance of that stripe at this part. The contractile substance of the muscle he describes 
as being, in the state of rest, arranged on either side of this median disk, with a clear 
fluid separating it from the terminal disks above and below. The enclosure of each 
muscle-element is completed at the sides by a lateral membrane. In contraction of the 
muscle Merkel describes the contractile substance as at first becoming diffused through- 
out the muscle-element, and finally becoming collected in the vicinity of the terminal 
disks. By what mechanism such locomotion is capable of producing shortening of the 
muscle is not explained^. 
Flogel, who for the most part employed muscle of Trombidium which had been treated 
with osmic acid, describes a fibre as divided into compartments, similar to those described 
by Krause, by means of transverse partitions ( Querwande ), which, however, he believes 
to be formed by the juxtaposition of granules interpolated at regular intervals in the 
course of the fibrils, which latter extend from end to end of the fibre, imbedded in a 
ground-substance wdiich is probably of a fluid nature. In the median portion of each 
muscle-compartment these fibrils, if I understand Flogel’s meaning aright, are more 
marked ( Sdulen ) than near the transverse partitions, in the immediate neighbourhood of 
which the substance is clear and homogeneous, but contains both above and below each 
transverse partition a row of minute granules (granule-layer) ; and since it may some- 
times be seen that each granule lies in the same longitudinal line as one of the minute 
columns in the central part, the two are probably parts of the same fibril. 
* “ Ueber die quergestr. Muskeln der Milben,” Schtiltze’s Archiv, viii. Nov. 1871. 
t “ Der quergestreifte Muskel,” Schultze’s Archiv, viii. Jan. 1872. 
X “ Mikroskop. Untersuchungen fiber die quergestr. Muskelsubstanz,” PflUger’s Archiv, vii. Jan. 1873. 
§ It is but fair to add that Merkel’s results are principally based upon observations on the so-called fibrils of 
the thorax of insects ; and these present in many respects a structure entirely different from that met with in 
the muscles of the legs, this apparent difference being due to a different arrangement of the non-essential sub- 
stance (compare p. 438). 
