Geology Reference
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scleroised female counterparts for sperm storage.
In other groups, transformaion of legs into
genitalia begins early in life, and proceeds gradu-
ally throughout the young stadia. Adult life may
last only a few months, or in some groups for
several years with a coninued patten of mouling
into larger body size but without increasing the
number of segments.
By far the great majoriy of known species
belong to the subclass Helminthomorpha, in
which one or both pairs oflegs of the 7th segment
are modified in males into sperm transfer sruc-
tures called gonopods. Before maing, the male
curves his body anteriorly so that the openings of
the vasa deerenia, located on or near the base of
the 2nd pair oflegs, can place a droplet of semen
(or a spermatophore) on the gonopod, from which
it will later be ransferred to the female genitalia
(also located just behind the 2nd pair of legs)
during the copulatory phase. Although the study
of millipede sexual biology is sill only at an early
stage, it is now known that a number of species
pracise fairly complex courtship rituals, some
involving stridulaion by the male, or the provision
of an edible secreion with which a female is lured
into a stance that will facilitate further advance by
the host animal. Of course, in a large number of
species, the male effects copulation simply by the
exercise of brute force, although even here com-
plicity of the female may often be noted.
It is well known that amongst many animal
groups the reproducive systems may remain the
most conservaive element of intenal anatomy, so
that any modiicaions reflect evoluionary events
of major importance; yet, on the other hand, those
parts involved with sperm transfer may represent
disincions at the species level with utter idelity.
This is especially well illustrated in arthropods:
the pedipalps of male spiders, the first pleopods of
larger crustaceans, and the terminalia of insects,
each of which are indispensable to the systemaist
working with such creatures. To this spectrum
may be added the gonopods of most millipedes,
some of which have developed pattens of such
compleiy as to challenge our comprehension of
their possible mode of uncion. So reliable are
the genitalia as indices of the validiy of species,
that they have understandably provided the raw
material of modem classificaions and, to a
regrettable extent, have been abused by over-
worked taxonomists of the past whose descrip-
ions of new species often consisted of a sentence
or two about size and coloraion, with the inevit-
able 'Gonopods as figured'. Far too often the
figure was totally inadequate, and in the early days
of diplopodology, before the value of gonopods
was appreciated, they were generally not
illustrated (or even menioned) at all. It can be
appreciated that when (about a century ago) spe-
cies, genera and families began to be based on
gonopod structure, many taxa published without
any knowledge of their genitalia came to represent
major problems especially as regards matters of
priority in nomenclature. A large part of modem
diplopod taxonomy sill consists of redescribing
the type material (when it eists at all) of the
earlier species which were the basonyms of genera
and families.
An addiional dificulty incurred by obsessive
reliance on gonopods in disinguishing species
was the tendency to neglect other character
systems that often reflected specific differences
more strikingly than genital features would do.
Realisaion of this interesing state of afairs
resulted in part from the study of Tanzanian
material, amongst which several species of a par-
icular genus from a single localiy were found to
differ from each other in size, coloraion and
details of the body surface in very clear-cut ways,
whilst the gonopods showed little or no difereni-
aion. Further studies have suggested that this
situaion represents an early stage in the process
of sympatric speciaion, perhaps iniiated by adap-
taion to microniches, in which selecive pressures
have affected overall body form more rapidly than
the genitalia have had the ability (or necessity) to
'catch up'. This phenomenon is especially evident
in the montane fauna of oxydesmid millipedes and
will be menioned especially in connecion with
that family, but it is noted also amongst genera of
the Spirosrepidae, for instance.
In general, however, most millipede taxonomy
remains heavily based on characters of the male
genitalia, and for this reason the collector is urged
to coninue his eforts aield to the point of ensur-
ing that at least a single male is preserved if at all
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