ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
143 
meter were : for the frog’s muscle 27-32, for the muscle of Dyticus 
20-24, for that of Hydrophilm 13 '5-16 ‘5. 
The muscle iu these experiments was prepared by Ranvier’s method, 
which consisted in scraping it down on both sides with the scalpel. 
The thinnest of the lamellm thus prepared might contain several super- 
posed layers of fibre, so that it became of importance if possible to 
observe the diffraction effect of the cross striation of the individual fibres. 
For the purpose of such experiments, teased preparations were made 
of muscle which had been kept for a long time in 93 per cent, alcohol, 
and these were mounted in a mixture of equal parts of glycerin and 
water. The method of observation was the same as before, except that 
the Abbe condenser was lowered so far that the image of the source of 
light was projected beneath the plane of the object. Owing to the 
different thicknesses of the object-holders for the various preparations, 
it was necessary in each case to readjust so that the image of the source 
produced by the condenser should always be at the same distance 
beneath the plane of the object. This was effected by first adjusting 
the Microscope upon the object, then lowering the body-tube always by 
the same amount (102 divisions of the micrometer screw = 0-48 mm.), 
and finally raising or lowering the condenser until the image of the 
source became sharply defined. In the following table are given the 
results of measurements on different muscle-fibres. 
Group. 
No. 
Object. 
Measure- 
ments. 
Limits. 
Mean. 
I. 
Grating on glass. 
1 
1 mm. in 100 divisions.. 
_ 
2 
2 
3 
„ 500 „ .. 
„ 1000 
— 
= 
10 
20 
•4 
Hylobius abietis 
4 
2 
2 
5 
Hydrophilus piceus .. 
4 
2 -5-3 -5 
2-9 
II. 
6 
Scarabxus laticollis . . 
4 
3 
3 
Old alcohol-muscle; 
7 
Vespa Crabro 
4 
3-5-5 
4-2 
teased preparations 
8 
Mclolontha vulgaris .. 
4 
4 • 5-0 
5 
in equal parts of 
9 
Dyticus marginalis . . 
4 
6-8 
7 
glycerin and water. 
10 
Dana cscul., stretched .. 
8 
6-8 
71 
11 
Delis domestica 
4 
10-12 
11-1 
12 
Dana esculenta 
4 
11-2-12 
11-9 
By comparing the numbers obtained for tho muscle-fibres with 
those for the gratings, we have as mean distance of the strife, since 
these are inversely proportional to the linear distances of the spectra, 
for the unstretched frog’s muscle p 2 . jjtq = 1 • 68 p, for the stretched 
muscle p 2 . ^ = 2*82 p, for the muscle of EydropMlus 7 p, for that 
of Scarabseus 6-f /a, and for that of Eylobius 10 p. These numbers, 
however, are based on tho assumption that the muscle-fibres are similar 
to simple gratings with equal parallel and equidistant spaces. Such an 
assumption is approximately correct for tho frog’s muscle in which the 
striae Z (Rollett’s notation) are only visible with great difficulty or not 
