184 THE AMERICAN MONTHLY [Octobed 
be in good sections, enough can be seen to leave no doubt as to its relation 
to the remainder of the organ. It is thus determined to be a sheath, which 
invests and holds together the parts within. Such membranous sheaths sur- 
round very many of the organs of animal bodies; sometimes threads run in 
from the sheath or capsule to become twined around the parts inside, but 
there is no evidence that such is the case in’ Cambarus, unless to a very 
slight extent. The capsule belongs to a system of tissues in the body whose 
purpose is to bind together parts too delicate to hold themselves together, 
and it is called the supporting system or the connective tissue system. 
The fine structure or the cellular structure of the sheath itself cannot be 
determined from the inspection of perfectly vertical sections; but, since 
many of the sections in which the capsule shows will not be vertical to it, a 
more or less perfect surface view of the capsule can at times be obtained and 
the composition of the capsule determined. But a very much better way to 
arrive at this result is to especially prepare a bit of the capsule for examina- 
tion, which may readily be done in the following manner :—Carefully lift 
off from the surface of an undisturbed portion of the liver of a specimen 
which has been for some time in alcohol, whether previously preserved with 
other reagents or not, a portion of the capsule, pulling it about as little as 
possible. With a pair of fine, very sharp scissors snip out of the disengaged 
part of the capsule a piece about an eighth of an inch square and transfer it 
to a watch-glass containing 70% alcohol. From this point it should be 
manipulated with a section-lifter and with all possible delicacy. Transfer it 
from the 7o per cent. alcohol to a bath of borax-carmine and leave it for a 
few minutes ; five or ten minutes will probably be long enough. 
From the borax-carmine transfer for one minute, or about that time, to wash- 
ing solution (H. cl., 2 per cent.-++ 70 per cent. alcohol, 98 per cent.) Trans- 
fer to 70 per cent. alcohol, thence to 95 per cent. alcohol, thence to 100 per cent. 
alcohol, thence to pure turpentine or oil of cloves, thence to slide, and mount 
in balsam as usual. This course will result in the production of a surface 
exposure of the bit of capsule ready for examination. Examination with a 
power of 150 diameters will show the membrane to be dotted throughout its 
entire extent with nuclei, somewhat evenly dispersed in a single layer, thus 
allowing one to form a fair inference as to location of the boundary of the 
cells to which the nuclei belong. But the walls of the cells are so very dim 
that they cannot generally be seen after this treatment. We must think, then, 
that the capsule is made by the close juxtaposition of cells in one layer to form 
an expanded sheet, which may be used to wrap about delicate organs for their 
protection. In this form it is one of the varieties of connective tissue ; some 
others beside it will be found to occur in the body of Caméarus. I may say 
here that the capsule affords an excellent example of one of a class of structures 
called by the histologists ‘ tissues.’ A tissue is usually defined as an ‘ assem- 
blage of similar cells.’ It is the feature of a tissue that its cells are similar in 
both structure and function, and in this capsule we have a good instance of a 
tissue. The term is often loosely and improperly used with a less definite 
signification for the substance of which either animals or plants are composed. 
2. The tubules of the gland.—An examination of the light-colored 
star-shaped bodies in the gland will soon convince the reflecting observer of 
the section that these are empty spaces, and that they are of the same nature as 
elongate bodies, whatever that nature maybe. That these spaces are the lumina 
of the tubules may not at first be manifest, but I think it must become so 
after a study of their position throughout the section. At A there is seen 
a central opening with several spaces leading out from it, one of them, B, 
running down as an elongate space, bounded by a peculiar wall. The wall 
is bounded on the side farthest from the space by a sharp boundary line which 
