ers are remarkable for the
concentration and specialization of their structure, which is
accompanied with high physiological efficiency. The larger species of
Bird's Nest Spiders (_Avicularia_), the opisthosoma of which is as
large as a bantam's egg, undoubtedly attack young birds, and M'Cook
gives an account of the capture in its web by an ordinary house spider
of a small mouse. The "retrovert" or bent-back first pair of
appendages is provided with a poison gland opening on the fang or
terminal segment. Spiders form at least two kinds of
constructions--snares for the capture of prey and nests for the
preservation of the young. The latter are only formed by the female,
which is a larger and more powerful animal than the male. Like the
scorpions the spiders have a special tendency to cannibalism, and
accordingly the male, in approaching the female for the purpose of
fertilizing her, is liable to be fallen upon and sucked dry by the
object of his attentions. The sperm is removed by the male from the
genital aperture into a special receptacle on the terminal segment of
the 2nd prosomatic appendage. Thus held out at some distance from the
body, it is cautiously advanced by the male spider to the genital
aperture of the female.

[Illustration: FIG. 63.--Ventral view of a male mygalomorphous spider.

I to VI, The six pairs of prosomatic appendages.
a, Copulatory apparatus of the second appendage.
b, Process of the fifth joint of the third appendage.
M, Mouth.
pro, Prosternite of the prosoma.
mes, Mesosternite of the prosoma: observe the contact of the coxae
of the sixth pair of limbs behind it; compare _Liphistius_ (fig.
61) where this does not occur.
stg, Lung aperture.
gn, Genital aperture.
a, Anus with a pair of backwardly migrated spinning appendages on
each side of it; compare the position of these appendages in
_Liphistius_ (fig. 61).

(From Lankester, "Limulus an Arachnid.")]

[Illustration: FIG. 64.--_Liphistius desultor_. Under side of the
uplifted genital or first opisthosomatic somite of the female; g,
genital aperture; p, pitted plate, probably a gland for the secretion
of adhesive material for the eggs; l, the edges of the lamellae of the
lung-books of the first pair.

(Original drawing by Pocock.)]

For an account of the courtship and dancing of spiders, of their webs
and floating line