Page:The Zoologist, 4th series, vol 3 (1899).djvu/563

Rh purpose is similar. Thus Partridges "roost close to the ground, and sleep with their heads tucked close together. A covey in this position represents little more than a mass of feathers. They always spend their nights in the open, for protective reasons. Birds which do not perch would soon be extinct as a species were they to seek the protection of woods and hedgebottoms by night. Such ground generally affords cover to vermin—Weasels, Polecats, and Stoats."

An active or aggressive mimicry is probably the explanation of the observation recorded by Mr. Woodford, made on Peel Island, Moreton Bay, where in the yellow-and-white blooms of different shrubs he found Spiders which were practically concealed by their assimilative colouration to these flowers. They were seen to attack the Bees which visited the bloom. M.E. Heckel, of Marseilles, has described an interesting case, which may be frequently seen in the South of France. The Spider, Thomisus onustus, is often found in the flowers of Convolvulus arvensis, where it hides itself for the purpose of snaring two Diptera, Nomioides minutissimus and Melithreptus origani, on which it feeds. Convolvulus is abundant, and three principal colour variations are met with—there is a white form, a pink one with deep pink spots, and a light pink form with a slight greenishness on the external wall of the corolla. Each of these forms is particularly visited by one of three varieties of Thomisus. The variety which visits the greenish form has a green hue, and keeps on the greener part of the corolla; that which lives in the white form is white, with a faint blue cross on the abdomen, and some blue at the end of the legs; the variety which lives in the pink form is pink itself on the prominent parts of the abdomen and legs. The colour, however, is of an assimilative nature, as M. Heckel found that when the pink, white, green, and yellow varieties of the Spider are confined together in a box they all become nearly white.

That undoubted examples of active mimicry are to be found among the Arthropoda will occur to the mind of every naturalist at the mention of "Trap-door Spiders." It is unnecessary to