Chapter XV: Appendix: To the Volume

HINTS ON THE PREPARATION OF SPECIMENS.

_To preserve Spongillidæ._--Spongillidæ must be preserved dry or in very strong alcohol. Formalin should not be used.

_To clean siliceous sponge spicules._--Place small fragments of the dried sponge (if alcohol is present, the reaction is apt to be violent) in a test tube, cover them with strong nitric acid and boil over the flame of a Bunsen burner or small spirit lamp until the solid particles disappear. Add a large quantity of water to the acid and filter through pure cellulose filter-paper, agitating the liquid repeatedly. Pass clean water in considerable quantities through the filter-paper and dry the latter carefully; place it in a spirally coiled wire and ignite with a match, holding the wire in such a way that the spicules released by the burning of the paper fall into a suitable receptacle. They may then be picked up with a camel's-hair brush and mounted in Canada balsam.

_To examine the skeleton of a Spongillid._--Cut thin hand-sections with a sharp scalpel, dehydrate if necessary, and mount in Canada balsam.

_To prepare gemmules for examination._--Place the gemmules dry in a watch-glass with a few drops of strong nitric acid. When gas is given off freely add water in considerable quantities. Remove the gemmules with a camel's-hair brush to clean water, then to 50%, 70%, 90% and absolute alcohol in succession, leaving them for an hour in each strength of spirit. Clear with oil of cloves and mount in Canada balsam.

_To ascertain the presence of bubble-cells in the parenchyma of a Spongillid._--Tease up a small piece of the sponge with a pair of needles, mount under a thin cover-slip in strong spirit, and examine under a high power of the microscope.

_To preserve Hydra in an expanded condition._--Place the polyp in a watch-glass of clean water and wait until its tentacles are expanded. Heat a few drops of commercial formaldehyde and squirt the liquid while still hot at the _Hydra_, which will be killed instantaneously. Remove it to a solution of formaldehyde and spirit of the following formula:--

Commercial formaldehyde 1 part.
Absolute alcohol 3 parts.
Distilled water 7 parts.

Then pass the _Hydra_ through 50% and 70% alcohol and keep in 90%.

_To examine the capsules of the nettle-cells._--Place a living _Hydra_ in a small drop of water on a slide and press a thin cover-slip down upon it.

_To preserve freshwater polyzoa in an expanded condition._--Place the polyzoa in a glass tube full of clean water and allow them to expand their tentacles. Drop on them gradually when they are fully expanded a 2% aqueous solution of cocaine, two or three drops at a time, until movement ceases in the tentacles. Then pour commercial formaldehyde into the tube in considerable quantities. Allow the whole to stand for half an hour. If it is proposed to stain the specimens for anatomical investigation, they should then be removed through 50% and 70% to 90% alcohol. If, on the other hand, it is desired to keep them in a life-like condition they may be kept permanently in a solution of one part of commercial formaldehyde in four parts of water. Care must be taken that the process of paralyzing the polypides is not unduly prolonged, and it is always as well to preserve duplicate specimens in spirit or formalin with the lophophore retracted.

_To prepare statoblasts for examination._--Place the statoblasts for a few minutes in strong nitric acid. Then remove the acid with water, pass through alcohol, clear with oil of cloves, and mount in a small quantity of Canada balsam under a cover-slip, taking care that the statoblasts lie parallel to the latter.

ADDENDA.

The following addenda are due mainly to an expedition to the lakes of Kumaon in the W. Himalayas undertaken by Mr. S. W. Kemp in May, 1911.