THE LEG-MUSCLES OE THE WATER-BEETLE. 
433 
by and enclosed in a network of clear bright lines. It would seem probable, however, 
that these areas are due to the action of the saline solution; for, as Kolliker* has 
pointed out, they do not occur if the section is examined fresh without addition. A 
line punctuation has been described within Cohnheim’s areasf ; this is, however, better 
seen when the limits of the areas are less marked. 
It is but seldom that I have been successful in obtaining Cohnheim’s areas in sections 
of Dytiscus- muscle. On the other hand, it is not at all uncommon to find fibres the 
section of which presents the appearance of dark lines, with bright intervals, radiating 
from the central protoplasm (fig. 4). The lines are equidistant from one another, and 
now and then divide dichotomously as they proceed outwards towards the sarcolemma. 
The picture presented irresistibly brings to mind the appearance of a transverse section 
of an incisor tooth as seen with a low power. The addition of fluid is not necessary for 
the production of this appearance, as seems to be the case with the areas of Cohnheim. 
As regards an explanation of these appearances, I am inclined to think that the 
section becomes mapped out into areas of Cohnheim owing to a change which takes 
place in the intermediate substance between the muscle-rods, whereby, instead of being 
evenly diffused, this tends to collect at definite lines in the fibre, the rods which are 
enclosed by these becoming on this account more closely grouped, so as eventually to 
be no longer separately distinguishable. 
The radiated appearance above described I was at one time inclined to explain in a 
similar manner; it may, however, be due to a slight inclination of the muscle-rods 
towards the axis of the fibre ; in this manner they would appear to overlap one another, 
and so produce the effect of radiating lines. 
V. Ground-substance of Muscle — Cause of the Cross Striae. 
The muscle-rods do not form by their agglomeration the muscular fibre, but are 
distinctly seen to be imbedded in a ground-substance , the characters of which we must 
now discuss. 
This substance appears, as a rule, in longitudinal view not homogeneous, but, as 
before mentioned, to consist of alternating disks composed of two distinct materials, of 
which the one in which the heads of the muscle-rods lie is bright and clear, whereas 
that which contains their shafts is dim. The fact that the bright transverse bands are 
often seen to present a slight bulging opposite each of the rod-heads, and that when 
the latter become of the same diameter as the shaft (so as to be no longer seen as distinct 
objects) the bright bands also entirely disappear, would seem to show that the bright 
appearance is an optical effect produced by the presence of the globular heads. 
That such an explanation is a possible one is shown by the following experiment : — 
A strong solution of gelatine is taken, and having been rendered fluid by heat, a few 
drops of oil are added and the mixture is thoroughly shaken for a few minutes. By 
* “Ueber die Cohnheim’schen Felder der Huskel-Querschnitte,” Zeitschr. f. wiss. Zool. Band xvi. (1866). 
t Kollikee, Joe. cit. Engelmaxn, “ Mikroskopische Untersuchungen fiber die quergestreifte Muskel- 
aubstanz,” Pfle gee’s Archiv, Jan. 1873. 
