EVAPORATION IMBEDDING-MASSES

such as stings and ovipositors, retaining all the parts in their
natural positions.
262. Copal-Imbedding (von Koch's method ').-Smallpieces
of the object are stained in the mass and dehydrated with
alcohol. A thin solution of copal in chloroform is prepared
by triturating small fragments of copal in a mortar with fine
sand, pouring on chloroform to the powder thus obtained,
and filtering. The objects are brought into a capsule filled
with the copal-solution. The solution is now slowly evapo-
rated by gently heating the capsule on a tile by means of a
common night-light placed beneath it. As soon as the solu-
tion is so far concentrated as to draw out into threads that
are brittle after cooling, the objects are removed from the
capsule and placed to dry for a few days on the tile, in order
that they may more quickly become hard. When they have
attained such a degree of hardness that they cannot be in-
dented by a finger-nail, sections are cut from them by means
of a fine saw. The sections are rubbed down even and
smooth on one side with a bone, and cemented, with this side
downwards, to a slide, by means either of Canada balsam or
copal-solution. The slide is put aside for a few days more
on the warmed tile. As soon as the cement is perfectly hard,
the sections are rubbed down on a grindstone, and then on a
hone, to the requisite thinness and polish, washed with water,
and mounted in balsam.
The process may be varied by imbedding the objects un-
stained, removing the copal from the sections by soaking in
chloroform, decalcifying them if necessary, and then staining.
It is sometimes a good plan, after removing the copal, to
cement a section to a slide by means of hard Canada balsam,
then decalcify cautiously the exposed half of the specimen,
wash, and stain it. In this way, von Koch was able to
demonstrate the most delicate lamelhe of connective tissue
in Isis elongata.
1 ' Zool. Anz.,' 2 (vol. i, 1878), p. 36.

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