442 
ME. E. A. SCHAFER ON THE MINUTE STRUCTURE OF 
and that such fibres are capable of repeatedly undergoing the most complete spontane- 
ous contraction: indeed after the death of the fibre the distinctness of the picture 
becomes always very much impaired, and often the structural appearances become 
entirely obliterated. Further, I may remark that since reading Engelmann’s article I 
have taken what opportunities offered of examining the muscles of minute aquatic 
Crustacea and insects whilst still in the living body, and as a result of such examination 
may state that, in spite of the difficulties to observation offered by the presence of the 
chitinous integument and the small size of the muscular elements, there is no great 
difficulty, with a good immersion-glass, in seeing that they possess an apparent longi- 
tudinal fibrillation. If further proof were needed, it is to be found in an exceedingly 
interesting paper by Professor Wagener*, in which the appearances observable in the 
muscles of the Corethra- larva in the living state are fully detailed. But to return to 
our subject. 
The transverse membrane of Krause and the narrow disk of intermediate substance 
(. Zwischensubstanz ) of Heppner would seem to be referable to the heads of two contiguous 
series of muscle-rods, which, as before stated, often meet in the middle of the clear 
stripe. The terminal disks of Merkel, the granule-layers of Flogel, and the Neben- 
scheiben of Engelmann are also, I think, to be referred to the same structures, which are 
by these observers correctly differentiated into two rows. The Stdbchen of Krause and 
Engelmann and the Sdulen of Flogel would appear to correspond with the shafts of 
the muscle-rods of my description. There remain the Mittelsclieibe of Merkel and 
others, and the line between each two muscle-series, which is to be seen only in very 
extended conditions of the fibre ( Querwand , Flogel; Zwischenscheibe, Engelmann). To 
explain these appearances, it is necessary to revert to what has been said with regard to 
the minute oil-globules in the experiment before mentionedf . It was there noted that 
the bright halo around each oil-globule is often seen to be bounded by a marginal 
line rather darker than the rest of the field, and probably to be explained by interference. 
The granules in muscle (rod-heads) must each have a similar effect upon the light ; and 
since they are disposed in rows, so that their bright haloes coalesce into bright bands, 
these darker margins must similarly coalesce into dim bands. Consequently the 
edges of the broad dim stripe (Querscheibe, Plate XXXIII. fig. 1 , a) of muscle will be 
caused to appear somewhat darker J than the central part ( e ), which latter has been for 
this reason taken for a distinct layer [Mittelsclieibe). Of course in the case of a mus- 
cular fibre all these effects are very much more marked than if we had to deal with a 
single series of granules, since other rows which are somewhat out of focus contribute 
to increase the result §. 
* “ Ueber einige Erscheinungen an den Muskeln lebender Thiere,” Sitzungsb. d. Gesellseh. z. Beforderung 
der gesammten Naturwissenscbaften zu Marburg, No. 8, August 1872. 
f See footnote, page 434. 
t The contrast with the bright band would probably tend to enhance this effect. 
§ When a very strong light is employed coloured fringes are often visible on the confines of the dim and clear 
stripes, and doubtless result from such interference effects as I have indicated. 
