THE SPIDERS OF EPPING FOREST. 183
V. A Systematic List of the Spiders of Epping Forest,
including brief descriptions of families,
genera and species.
I.—ANATOMY.2
Body. The body or trunk consists of two well-defined parts,
Cephalo-thorax and Abdomen, connected by a slender
Pedicle or waist.
Cephalo-thorax. This is the anterior great division of the
body, consisting of the Caput or head, and the Thorax.
These two parts are fused together, a more or less
distinct linear impression usually indicating the junction.
Traces of original segmentation of the thorax are as a rule
apparent in the form of depressed lines termed lateral
impressions which converge upon a more or less distinct
central impression (occasionally absent). The integument
of the cephalo-thorax is of a more or less firm and
resistant character; but in the case of some species in
which the abdomen is protuberant anteriorly, the
posterior portion of the thoracic integument becomes of
a somewhat pliant nature. The caput is more or less
wedge-shaped posteriorly. Upon the posterior portion
of the upper surface of the thorax is occasionally found
a stridulating organ The length of the cephalo-thorax
should be taken as implying the direct distance between
the lower edge of the clypeus and the central part of
the posterior margin of the thorax. This measurement
is best made by means of an accurate divider with
curved needle points.
Connected with the cephalo-thorax are the follow-
ing structures, which are described separately:—Eyes,
Sternal-plates, Falces, Palpi, Legs.
Eyes. The eyes of spiders are invariably simple and are
normally eight in number. In a few British species
only six are present, whilst in some exotic spiders the
number is still further reduced to four or occasionally
two. Two forms of eyes are found, which Mons. E.
Simon, conceiving a difference in their respective
functions, designates diurnal eyes and nocturnal eyes.
2 See Plates VII. and VIII., with the explanations thereof on pp. 180-90 post.