inedible by the possession of sharp
spines and chitinous plates, and also those that mimic other specially
protected creatures.

The females of the specially protected group are characterized by the
following attributes:

Their inedibility, which they owe to a more or less coriaceous
epidermis and an armature of strong sharp spines (Fig. 6).

Their brilliant colors--glistening black and white, yellow, fiery
gold, metallic silver, rose-color, blue, orange and blood-red.

Their habit of hanging always exposed in the centre of the web.

[Illustration: FIG. 6.--GASTERACANTHA CREPIDOPHORA (from Cambridge).]

In an interesting discussion of the protective value of color and
marking in insects, Poulton says that "the smaller convergent groups
of nauseous insects often present us with ideally perfect types
of warning patterns and colors--simple, crude, strongly
contrasted--everything subordinated to the paramount necessity of
becoming conspicuous," the memory of enemies being thus strongly
appealed to.

This proposition is well illustrated by the Gasteracanthidae. Among
larvae the warning colors are almost invariably black and white, or
black (or some very dark color), in contrast with yellow, orange and
red. These are the colors that also constantly recur among the
Gasteracanthidae.

Cases that may be more justly considered exceptions to the rule that
these hard, uneatable spiders are conspicuous are such species as
Acrosoma rugosa (Fig. 7). One of this species was sent me by Mrs.
Treat last summer. It lived for several weeks in my window, making no
regular web, but hanging among a few irregular strands. It ate
nothing, although provided with insects, but drank greedily of water.
It might seem that its black and white coloring would make it
conspicuous, but in connection with its irregular shape and its way of
hanging motionless in the web it had the opposite effect.

We have no reason to suppose that the class represented in rugosa is
like that touched upon by Poulton, in which very protectively colored
larvae suddenly assume a terrifying aspect on the near approach of an
enemy; still they do enjoy a kind of double protection.

[Illustration: FIG. 7.--ACROSOMA RUGOSA. Left-hand figure female,
right-hand figure male (from Emerton).]

They are inconspicuous, and thus likely to escape attack, but in case
they are attacked they have still the advantage of being quickly
rejected. This experience cannot be as fatal t