Their Collection and Investigation. 53
relative length of these appendages in the flagellate class
is of high importance, but is ascertainable in many cases
only in connection with a prolonged and careful examination.
The manner in which food is ingested by the Flagellata,
whether by a distinct mouth or through the general surface
of the body, should be accurately determined. Such obser-
vation may be greatly facilitated by the addition to the water
of a little carmine or other pigment from an ordinary box of
water-colours.4 Special attention should be bestowed upon
the reproductive phenomena. All Infusoria multiply rapidly
by simple subdivision or fission, and it should be noted
whether this fissive process takes a longitudinal, transverse,
or oblique direction. Some forms give birth to living
embryos, while among the Flagellata it generally happens
that the whole body-mass splits up into spore-like elements.
Sometimes this reproductive process is preceded by the
fusion or conjugation of two or more animalcules. It should
be the object of the investigator to ascertain and register as
many data as possible connected with these several phenomena.
4 [Until the last few years it was thought impossible to preserve most of
the Infusoria for future study and reference, but Mr. Kent has elsewhere
described (' Manual of Infusoria,' p. 113) the value of osmic acid as an
agent for their conservation. A drop of the solution in distilled water
(1 per cent. solution) should be placed on the covering glass before the
latter is placed over the specimen. All structures, such as cilia, cirri
and flagella, the internal endoplast, and in Euglenia and its allies, the
colours also, are stated by Mr. Kent to be perfectly preserved. The
animalcules thus killed may be fastened down as permanent preparations,
without the addition of any other preservatives, and may be stained with
the ordinary agents, haematoxylin, eosin, picro-carmine, &c., known to
histologists. The objection to osmic acid is that it is very costly and
excessively poisonous, its vapour having an intolerable odour, and
attacking the eyes in a very painful manner. A solution of iodine in
potassium iodide is without these objections, and acts in a similar, and
almost equally efficient, manner. Another harmless agent is afforded,
according to M. du Plessis, by a saturated solution of potassium perman-
ganate; and for the preservation of the stalked Vorticellidae very dilute
spirit (1 in 10) is recommended. For manipulative details the student
may usefully consult Huxley and Martin's 'Practical Biology,' Carpenter
and Beale on the microscope, and Schaffer's 'Practical Histology,' in
addition to Mr. Kent's marinum opus, above cited.—Ed.]