MIMICRY. 638 



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 hedge- 

 bottoms 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 con- 

 cealed by their assimilative colouration to these flowers. They 

 were seen to attack the Bees which visited the bloom. f 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, J 



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 



* J. Watson, ' Poachers and Poaching,' p. 9. 



f 'A Naturalist among the Head-Hunters,' p. 70, note. 



{ ' Nature,' vol. xliv. p. 451, 



