THE SPIDERS OF EPPING FOREST.
191
find perfect gradations from the most ancient stock to the most
highly specialised species. The early attempts at a systematic
classification, not only of the Araneae but of almost all the
Natural Orders of animals, were more or less of the nature of an
arrangement, founded upon the most evident structural differences,
intended to facilitate the conversion of a visibly heterogeneous
order into several groups possessed of something like homo-
geneity. With the general acceptance of the various theories of
evolutionary science, the systematist has not only endeavoured to
elucidate the relation existing between order and order, or family
and family, but has essayed to trace the development, through
successive stages, of the most highly specialised creatures from
the primary representatives of the group under his consideration.
The order Araneae is, broadly speaking an exceedingly homo-
geneous one and the difficulty of satisfactorily characterising the
various groups is exaggerated by the simplicity of structure
exhibited. It should be borne in mind that the development of a
group of animals from an original stock cannot be truly repre-
sented by any linear arrangement but rather by a genealogical
"tree," the "root" corresponding to the elementary, and the
"twigs" to the most highly specialised forms. In dealing with
the evolutionary development of the Araneae I am aware that I
am venturing upon dangerous ground. In this matter modern
araneologists are not by any means agreed, as a very cursory
glance at the more recent English and Continental publications
will show; and I trust, therefore, that the accompanying diagram
(Plate IX.) may be regarded simply as expressing the opinion of
a single individual.
ORDER ARANEAE.
Head and thorax fused to form a single piece. Eyes simple. Abdomen
almost invariably non-segmented, connected with the thorax by a slender
pedicle, terminated by several pairs of spinners, each furnished with numerous
spinning tubes. Respiratory organs consisting of laminal tracheae and tube
tracheae, both kinds being usually found in one individual. (The tube tracheae
are occasionally absent; and, very rarely, the laminal tracheae are wanting).
Reproductive organs of both sexes situated between the anterior spiracular
openings, but the ejactorial apparatus of the male is connected with the
terminal joint of the palpus. Falces consisting of a stout basal joint and a
movable fang, pierced with a channel and capable of injecting a poisonous
fluid. Sternal plates two in number. Palpus of the female pediform. Legs
eight, each consisting normally of seven joints.