10
A. MACFADYEN
or examined. A full treatment of this topic is not praticable here, but a
few notes may perhaps be of assistance to the newcomer.
Most small arthropod material is ultimately examined in the form of
a suspension of animals in specimen tubes (vials) containing a fixative
solution such as 80% alcohol. Some arthropods especially Collembola,
do not sink readily in such solutions and Gisin (1960) gives a formula for
a solution in which they sink more readily. This contains much ether and
cannot be used in most Tullgren-type funnels, which necessitates
manipulation of the samples to change the fluid. An alternative which
the author has found quite satisfactory is to place the corked samples in
an oven or other warm place at about 50°C until the fixative has
warmed. Usually all Collembola sink under these circiimstances but if
any are still floating after gently swilling the fluid in the tube they can
be sunk by a single drop of ether. Once all arthropods have sunk the
bulk of the samples can be safely reduced by decantation.
It is still true to say that no permanent microscopic preparation
method exists by which taxonomically critical material can be preserved indefinitely. Probably the best “permanent” methods are the
ringed lactic acid preparation of Gisin (1960) for Collembola, the use of
Gum Chloral media (see Evans, 1955) for the more robust mites, and of
California mountant (Baker and Wharton, 1952) for more delicate ones.
But it is far safer to keep whole samples and important specimens in
small tubes corked with cotton wool - or better Polyporus (Hobart,
1956) and submerged in an outer vessel containing 80% alcohol. Labels
are best written in soft pencil on good quality card because some indian
inks are not stable. Temporary mounts in lactic acid are then used to
examine specimens when required (Evans, 1955). Further details on
mounting methods are given by Kevan (1955) and Kuhnelt (1961).
A number of quite complicated techniques have been devised for
counting submerged animals under the microscope, including the long
chamber driven by a gramophone motor under a binocular microscope
used by the Freshwater Biological Association for plankton counting
and the special nematode counting chambers described by Williams and
Winslow (1955) with ruled squares for aliquoting and labyrinths to
facilitate searching. Many workers use a ruled, flat-bottomed vessel
and search each “lane” in turn. A most useful device is the “gliding
stage” (manufactured by W. Watson & Son Ltd) with which any glass
vessel can be moved in parallel lines beneath a microscope. Since it is
usually necessary to handle specimens and turn over larger species and
pieces of detritus, the author finds it more convenient either to push all
material to one side as it is counted and as the vessel is moved in parallel
lines or, alternatively, to pick out each specimen with fine Swiss watchmaker’s forceps. I n this way duplication of counts is avoided and no
A. MACFADYEN
or examined. A full treatment of this topic is not praticable here, but a
few notes may perhaps be of assistance to the newcomer.
Most small arthropod material is ultimately examined in the form of
a suspension of animals in specimen tubes (vials) containing a fixative
solution such as 80% alcohol. Some arthropods especially Collembola,
do not sink readily in such solutions and Gisin (1960) gives a formula for
a solution in which they sink more readily. This contains much ether and
cannot be used in most Tullgren-type funnels, which necessitates
manipulation of the samples to change the fluid. An alternative which
the author has found quite satisfactory is to place the corked samples in
an oven or other warm place at about 50°C until the fixative has
warmed. Usually all Collembola sink under these circiimstances but if
any are still floating after gently swilling the fluid in the tube they can
be sunk by a single drop of ether. Once all arthropods have sunk the
bulk of the samples can be safely reduced by decantation.
It is still true to say that no permanent microscopic preparation
method exists by which taxonomically critical material can be preserved indefinitely. Probably the best “permanent” methods are the
ringed lactic acid preparation of Gisin (1960) for Collembola, the use of
Gum Chloral media (see Evans, 1955) for the more robust mites, and of
California mountant (Baker and Wharton, 1952) for more delicate ones.
But it is far safer to keep whole samples and important specimens in
small tubes corked with cotton wool - or better Polyporus (Hobart,
1956) and submerged in an outer vessel containing 80% alcohol. Labels
are best written in soft pencil on good quality card because some indian
inks are not stable. Temporary mounts in lactic acid are then used to
examine specimens when required (Evans, 1955). Further details on
mounting methods are given by Kevan (1955) and Kuhnelt (1961).
A number of quite complicated techniques have been devised for
counting submerged animals under the microscope, including the long
chamber driven by a gramophone motor under a binocular microscope
used by the Freshwater Biological Association for plankton counting
and the special nematode counting chambers described by Williams and
Winslow (1955) with ruled squares for aliquoting and labyrinths to
facilitate searching. Many workers use a ruled, flat-bottomed vessel
and search each “lane” in turn. A most useful device is the “gliding
stage” (manufactured by W. Watson & Son Ltd) with which any glass
vessel can be moved in parallel lines beneath a microscope. Since it is
usually necessary to handle specimens and turn over larger species and
pieces of detritus, the author finds it more convenient either to push all
material to one side as it is counted and as the vessel is moved in parallel
lines or, alternatively, to pick out each specimen with fine Swiss watchmaker’s forceps. I n this way duplication of counts is avoided and no