20
A . M A C F A D Y E N
and by introducing known numbers of organisms. Litter copepods,
nematodes and enchytraeid worms are extracted with very low efficiency - of the order of 10% or less. Mites, Collembola and most other
arthropods are extracted very efficiently - of the order of 90% or more.
Snails and fly larvae, as a group, are extracted with considerably less
than 90yo efficiency. Each sample is spread over two layers of cotton
fillet net, whose openings are filled with delicate linty fibres. These tiny
fibres offer no serious impediment to the passage of animals but do
hold back most of the litter debris, resulting in a much cleaner extraction than is usual with Tullgren work - and a great saving in counting
time.
This apparatus resembles the “canister” extractor in using straightsided water-cooled containers and an aqueous medium for the purpose
of establishing high humidity; it is also the origin of the use of picric
acid fixative. The main differences are in the use of the cotton fillet net
which should show a distinct improvement in the cleanness of samples,
and in the use of a pulsating heat source in conjunction with light. The
advantages of this form of repellent stimulus will, no doubt, be justified
in the forthcoming paper.
A special extractor has been developed for obtaining spiders from
soil and litter, mainly in the form of undisturbec! turves, by E. Duffey,
of the Nature Conservancy, to whom the author is greatly indebted
for an account of the apparatus. This exploits the greater mobility
and better-developed senses of spiders, which are driven horizoiitally
out of the medium by a powerful electric-fire bar, the whole extraction
occupying only a day or so. The animals are collected in a trough containing dilute glycerine and pairs of spider-tight chambers are conveniently arranged on either side of fire bars with the troughs on the
outside. There is some difficulty, due to condensation, in handling wet
samples and the efficiency of the apparatus has not yet been exhaustively tested.
In most of the Tullgren-type extractors mentioned so far, heat, light
and desiccation in various combinations have been used as repellent
stimuli and in some, low temperatures and high humidities have been
added as attractants. There remains a very real need for more fundamental behavioural work on the various groups of arthropods with the
ultimate hope that a t least some sorting out of fauna will be achieved
by submitting samples to gradients of different factors: this is a longterm matter and beset by many technical difficulties (see Madge, 1961 ;
Macfadyen, 1962) and clear-cut behavioural responses are often hard
to demonstrate. At present the most hopeful approach seems to bethe
simultaneous application of as many repellent-attractant gradients as
possible, and certainly the use of combined heat and humidity gradients
A . M A C F A D Y E N
and by introducing known numbers of organisms. Litter copepods,
nematodes and enchytraeid worms are extracted with very low efficiency - of the order of 10% or less. Mites, Collembola and most other
arthropods are extracted very efficiently - of the order of 90% or more.
Snails and fly larvae, as a group, are extracted with considerably less
than 90yo efficiency. Each sample is spread over two layers of cotton
fillet net, whose openings are filled with delicate linty fibres. These tiny
fibres offer no serious impediment to the passage of animals but do
hold back most of the litter debris, resulting in a much cleaner extraction than is usual with Tullgren work - and a great saving in counting
time.
This apparatus resembles the “canister” extractor in using straightsided water-cooled containers and an aqueous medium for the purpose
of establishing high humidity; it is also the origin of the use of picric
acid fixative. The main differences are in the use of the cotton fillet net
which should show a distinct improvement in the cleanness of samples,
and in the use of a pulsating heat source in conjunction with light. The
advantages of this form of repellent stimulus will, no doubt, be justified
in the forthcoming paper.
A special extractor has been developed for obtaining spiders from
soil and litter, mainly in the form of undisturbec! turves, by E. Duffey,
of the Nature Conservancy, to whom the author is greatly indebted
for an account of the apparatus. This exploits the greater mobility
and better-developed senses of spiders, which are driven horizoiitally
out of the medium by a powerful electric-fire bar, the whole extraction
occupying only a day or so. The animals are collected in a trough containing dilute glycerine and pairs of spider-tight chambers are conveniently arranged on either side of fire bars with the troughs on the
outside. There is some difficulty, due to condensation, in handling wet
samples and the efficiency of the apparatus has not yet been exhaustively tested.
In most of the Tullgren-type extractors mentioned so far, heat, light
and desiccation in various combinations have been used as repellent
stimuli and in some, low temperatures and high humidities have been
added as attractants. There remains a very real need for more fundamental behavioural work on the various groups of arthropods with the
ultimate hope that a t least some sorting out of fauna will be achieved
by submitting samples to gradients of different factors: this is a longterm matter and beset by many technical difficulties (see Madge, 1961 ;
Macfadyen, 1962) and clear-cut behavioural responses are often hard
to demonstrate. At present the most hopeful approach seems to bethe
simultaneous application of as many repellent-attractant gradients as
possible, and certainly the use of combined heat and humidity gradients