MIMICRY. 181 
satisfactory. Many cases can be interpreted only by 
natural selection, those, namely, where from the first, 
before the imitation had begun, such a resemblance 
already existed between the imitating and imitated 
forms as to render confusion possible ; where, therefore, 
the resemblance so conducive to the preservation of 
those in which it was the strongest, needed only to be 
increased by natural selection. Darwin® is also of 
opinion “that the process probably has never com- 
menced with forms widely dissimilar in colour.” 
A peculiar, simpler and long known mimicry, is when 
animals have accommodated themselves in colour to 
their habitats in such a manner as not to attract the 
attention of their enemies, and likewise to deceive their 
prey. Who, in the days when he chased butterflies, did 
not learn how difficult it is to recognize certain evening 
and nocturnal flyers on the bark of trees, as they quietly 
sit with their dusky brown or gray-striped or speckled 
wings, outspread in a roof-like shape? The tree locusts 
and Mantide can look so deceptively like leaves or 
twigs, that it is only by the touch that one can be 
assured of their real nature. Wallace relates that one 
of the Phasmidz (Ceroxylus laceratus), which he obtained 
at Borneo, was so covered with pale olive-green excres- 
cences, that it looked like a stick covered with moss. 
The Dyak who brought him the animal declared that, 
although alive, it was really overgrown with moss, and 
the naturalist himself was only convinced of the con- 
trary by the closest examination. 
A remarkable example of advantagcous colouring, 
within easy reach of many of our readers, is exhibited 
in most species of the flat-fish (Pleuronectidz), now so 
