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XII. On the Minute Structure of the Leg-muscles of the Water-beetle. By Edward 
Albert Schafer. Communicated by Dr. Sharpey, V.P.B.S. 
Received March 13, — Read April 3, 1873. 
For the successful prosecution of the histological inquiry which forms the subject of 
the present communication, it is essential that the tissue to be investigated should be 
studied whilst still in the living condition, inasmuch as marked changes ensue very 
speedily after the death of the muscle, and still more speedily on the addition of 
reagents, even the so-called indifferent fluids, such as serum or ^ per cent, solution of 
common salt, being in this case inadmissible. The description, therefore, I have now 
to give is founded entirely on an examination of the living tissue. 
I. Appearance of Living Muscle in the state of rest. 
If we cut off a limb from one of the common large Water-beetles ( JDytiscus margi- 
nalis), remove a portion of muscle from the upper part, quickly separating the fibres 
somewhat from one another, by means of needles, on a glass slip, cover it without addi- 
tion, and examine the preparation so obtained with the aid of a very powerful immersion- 
objective (such as the No. 11 of Hartnack or the No. 3 of Zeiss), we find numerous 
muscular fibres presenting an appearance similar to that represented in Plate XXXIII. 
fig. 1. 
The well-known transverse bands are conspicuously seen, consisting of broader dim* 
stripes (a a) alternating with narrower bright ones ( b b), the latter exhibiting a trans- 
verse line of minute dots (c). These bands are now very generally admitted to repre- 
sent disks composed of two entirely distinct substances, arranged in successive series 
with their planes at right angles to the axis of the fibre ; and I shall, for convenience 
of description, adhere for the present to this notion, although, as I shall afterwards 
endeavour to show, the difference in appearance which they present may be accounted 
for otherwise than by regarding them as composed of different materials. 
To proceed with my description. Each disk of dim substance appears pervaded 
throughout by a number of excessively fine rod-shaped particles of uniform diameter, 
and rather darker in appearance than the substance of the disk which they traverse. 
These particles are arranged closely and very regularly, with their axes in a direction 
more or less parallel to that of the fibre ; they extend at either end into the neigh- 
bouring disks of bright substance, becoming somewhat less distinct as they pass 
* I use the word “ dim ” because, in fact, in living muscle at rest no such thing as a dark stripe occurs ; 
one part is only somewhat less bright than the other. 
3 M 
MDCCCLXXIII. 
