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58 II. DE ARACHNIDIS<br />
Pseudoscorpions are sometimes found with irregular tergites.<br />
Among spiders abnormal eye patterns are far from unusual, and almost<br />
everyone who has collected assiduously has come across specimens<br />
in which two eyes have merged into one, or in which one, two, or<br />
more eyes are m1ssmg.<br />
A very surprising example of unusual development has been shown<br />
to follow the submission of the eggs to the action of a centrifuge. Sekiguichi<br />
( 195 7) found that eggs thus treated for 20 minutes at 3,000 revolutions<br />
per minute showed duplication of the embryo. An example of<br />
one of his results is shown in Fig. 22.<br />
6. ONTOGENY: GROWTH 59<br />
Since sex is determined by the presence of one or more X-chromosomes<br />
in the male gamete, it is reasonable to suppose that an accident<br />
to, or a loss of, one of these chromosomes in the earliest stages of segmentation<br />
is responsible for abnormal development.<br />
In addition, a small number of intersex specimens have been found.<br />
Their peculiarity seems to be due to infection with the nematode<br />
Mermis, which partially destroys the gonads.<br />
FIG. 22. Duplicated embryo. After Sekiguichi.<br />
J uberthie ( 1963) pointed out that among the Opiliones abnormalities<br />
are rarely found in nature. He illustrated a single case of crossed tergites<br />
among Cyphophthalmi found in a specimen of Siro rubens, and<br />
commented on the fact that other recorded instances of teratology<br />
were limited among Opiliones to six species.<br />
He showed later ( 1968) that monstrosities were often produced if<br />
harvestmen's eggs were caused to develop at high temperatures. Eggs<br />
of Odiellus gallicus kept at 23-30°C produced cases of abnormal tergites,<br />
fused limbs, single eyes and an absence of eyes.<br />
Among the most fully described examples of abnormality are the<br />
appearances of gynandromorphs. The phenomenon of gynandromorphism<br />
is known among other invertebrates, and may be traced to its<br />
cause in the behaviour of the chromosomes. The number of gynandromorphs<br />
so far described barely amounts to 40 specimens, a much smaller<br />
number than has been found in some insect groups, and all but a very<br />
few of them have been spiders. Six types of gynandromorphism are<br />
possible, and all are known: they can be represented thus:<br />
(1\ M IF FI lV. '"I M (4) F (5) MFIMF<br />
F M<br />
lateral transverse crossed<br />
F<br />
Ivl<br />
.M F
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