Page:The Zoologist, 4th series, vol 3 (1899).djvu/496

466 supplied the insect food required for her young by carrying the excrements of the nestlings, as is the habit of some birds, and placing them with great care on different parts of a thorn bush.

"Apparently she had placed them thus to attract the flies, for each time she alighted on the bush she visited several, picking off the flies until she had enough to take back to her young." This may surely be taken as an instance of aggressive mimicry, consciously or actively pursued. According to Mr. Matthias Dunn, "Some fishes have such power over their own appearance that when they like they can change the colour of their skin in keeping with their surroundings. I have seen Surmullets, when going from the brown sand to the dark rocks, quickly change from one colour to the other, and I know of about forty other fishes which can do the like in more or less time." On this statement a writer has recorded that, in 1898 in the Aquarium at Concarneau, in Brittany, Turbot were seen "that gradually assumed the colour of the sand in which they were placed; so much so that it required a very keen eye to detect them lying at the bottom of the tank." Another writer has more recently remarked, in discussing "the beautiful and protective resemblance" which some insects "bear to their surroundings," that there can be no doubt that such species "possess an inherited and instinctive knowledge of this assimilation, and select such places as a protection against their natural enemies." Of course the suggestion of active mimicry must not be made too absolute. Thus Mr. Storrs Fox has proposed a very reasonable hypo-