Savory - Arachnida 1977

314
( i)
( ii)
( iii)
(iv)
(v)
V. HETEROGRAPHIA
It brings male and female together at the right season of the yea.r.
It ensures that mating takes place in an environment that will
suit the needs of the offspring.
It so synchronized physiological processes and mental moods
that both sexes may be excited and neither be aggressive.
It precludes possibilities of cross-fertilization.
It keeps rival males at a distance.
All this is perfectly true, and conclusions (iii) and (iv) are partiet~larly
applicable to the Arachnida. By conclusion (iii) there is imphed a
vitally important factor, the matter of time. .
The result to which these courtship activities usually lead IS the
amphimixis or union of ova and spermatozoa. In many . marine
organisms this is made probable by the liberation of the sperm m to the
water at the moment that the ova are shed, and the courtship helps to
ensure that these acts occur simultaneously, and when male and female
are close together. In the Arthropoda sperm is usually transferred ~o the
female in the form of a spermatophore, and in this way the semen IS n?t
diluted by the surrounding medium. This device was n?t an. a~achm?
invention. It is to be found among some of the Annehda; It Is, as It
were, hinted at by the Onychophora; is absent from the P.yc~~goni?a
and reappears among the Athropoda. It is therefore a pnmitive bwlogical
feature. . . .
In its simplest form the arachnid spermatophore IS a muCilagmous
mass of gametes, transferred to the female by the n:ale usir:g his
chelicerae, pedipalpi or legs. This type of sperm-transfer Is found m the
Solifugae and in some Acari. Indirect sperm-transfer by means of ~omplex
spermatophores deposited on the ground occurs among scorp~ons,
pseudoscorpions, Amblypgi, Uropygi, Schizomida a.nd some Acan .. In
these cases the main function of the spermatophore IS to prevent desiccation
of the semen and in these orders mating is preceded by a nuptial
dance. In this danc~ the male mesmerizes the females into a position in
which she can gather the spermatozoa into her genital orifice. In
spiders* and Ricinulei the spermatophore has been lost, and the sperms
are transferred by the palpal organs or the modified third leg of the
male respectively. .
The orders of Arachnida in which a spermatophore Is generally used
tend to show another common feature, namely an inclination towards a
cryptozoic mode of living, which is in itself.a pri~itive stage of evolution.
In clear contrast to these are the orders m which other methods are
37. COURTSHIP IN ARACHNIDA
315
found, the Araneae, Opiliones, Ricinulei and Solifugae. These include
the most advanced or specialized orders, that is to say, those that have
the longest list of characteristics peculiar to themselves. This supports the
idea that the spermatophore, valuable and efficient as it is, has been
abandoned by these orders; and these are also orders in which a more
open or phanerozoic life above the ground layer, in the forests or even
in the deserts is the rule.
Entry upon a new environment can seldom succeed unless some new
adaptive organ or other feature appears at the critical time, and this
may well be a part of the reason for the disappearance of the spermatophore.
How the changes took place are matters which, like many others,
remain part of tlw unknown factors of evolution.
• Cooke ( 1969) discussing the phylogeny of the male pcdipalp, has figured its original
condition, with a functional claw "which may have been used to transfer the spermatophore
to the female".