self-effacement on the one hand and
bluffing on the other. There can be little doubt that the power of
colour-change sometimes justifies itself by driving off intruders. Dr.
Cyril Crossland observed that a chameleon attacked by a fox-terrier
"turned round and opened its great pink mouth in the face of the
advancing dog, at the same time rapidly changing colour, becoming almost
black. This ruse succeeded every time, the dog turning off at once." In
natural leafy surroundings the startling effect would be much greater--a
sudden throwing off of the mantle of invisibility and the exposure of a
conspicuous black body with a large red mouth.

Sec. 4

Likeness to Other Things

Dr. H. O. Forbes tells of a flat spider which presents a striking
resemblance to a bird's dropping on a leaf. Years after he first
found it he was watching in a forest in the Far East when his eye fell
on a leaf before him which had been blotched by a bird. He wondered idly
why he had not seen for so long another specimen of the bird-dropping
spider (_Ornithoscatoides decipiens_), and drew the leaf towards him.
Instantaneously he got a characteristic sharp nip; it was the spider
after all! Here the colour-resemblance was enhanced by a
form-resemblance.

[Illustration: A. PROTECTIVE COLORATION OR CAMOUFLAGING, GIVING ANIMALS
A GARMENT OF INVISIBILITY

At the foot of the plate is a Nightjar, with plumage like bark and
withering leaves; to the right, resting on a branch, is shown a
Chameleon in a green phase amid green surroundings; the insects on the
reeds are Locusts; while a green Frog, merged into its surroundings,
rests on a leaf near the centre at the top of the picture.

B. ANOTHER EXAMPLE OF PROTECTIVE COLORATION OR CAMOUFLAGE

A shore scene showing Trout in the pool almost invisible against their
background. The Stone Curlews, both adult and young, are very
inconspicuous among the stones on the beach.]

But why should it profit a spider to be like a bird-dropping? Perhaps
because it thereby escapes attention; but there is another possibility.
It seems that some butterflies, allied to our Blues, are often attracted
to excrementitious material, and the spider Dr. Forbes observed had
actually caught its victim. This is borne out by a recent observation by
Dr. D. G. H. Carpenter, who found a Uganda bug closely resembling a
bird-dropping on sand. The bug actually settled down on a bird-dropping
on sand, and caught a blue butterfly which came