28o iMIMICRV AND NATURAL SELFXTION 



perhaps the most [powerful ar^aiment of all in favour of 

 an interpretation based on the theory of Natural Selec- 

 tion. If these resemblances are attained by selection 

 because the\' are advantajjeous in the struiji'le for life, we 

 sliould expect to fnul that they are produced in a i^reat 

 variety of ways ; for one species would reach the bene- 

 ficial end by one path pointed out to it by the structure 

 it possessed at the beginning and ])y the trend of its 

 variation, while another species with a very different initial 

 structure would reach the same end by a widely different 

 path. Thus many Diptera, for example sj^ecies of Ccria, 

 gain a superficial resemblance to wasps by a narrowing 

 in the anterior abdominal reerion which suo-^ests the 

 characteristic peduncle of a 1 1) nienopterous insect. On 

 the other hand, Lon<''icorn beetles of the <':enus Obcrca 



CD O 



gain the same effect by a patch of white which obliterates 

 the anterior al)dominal region with the exception of 

 a small linear remnant representing the peduncle.^ In 

 brilliant illumination the white markincr is not seen as 

 ])art of the insect. The resemblance of the Locustid 

 iMyr))ieiOpJia)ia fallax to an ant is produced in the same 

 manner.- The Homopterous family Alcuibracidac are 

 characterized by an enormous growth of the dorsal region 

 of the pro-thorax, which spreads backwards and in many 

 species covers the insect like a shield. In the American 

 species which mimic ants, this shield, and not the insect 

 beneath it, becomes ant-like. Some of the larval Alcni- 

 bracidac are laterally com]:)ressed, becoming in the dorsal 

 region as thin as a leaf, and the body is green like a leaf, 

 while the head anel legs are brown. The whole appear- 

 ance is singularlv like that of tlie tropical American ant 

 At (a {Occodo?)ia) ccpJialotcs, carrying its leaf vertically in 

 its mandibles, and thrown over its back, so that the brown 

 head, legs, and part of the body are seen beneath the 

 green burden.^ It is manifestly absurd to attempt to 



* See R. Shc'lford in Pioc. Zool. Soc. Lond., 1902, pp. 238-40, plate 

 xix, figs. 13, 14, 15. 



^ See pp. 256-7 of the present volume, together with Fig. 5, p. 258. 



^ See description and figure of a specimen found by Mr. \V. L. Sclater 

 in British Guiana. Toulton, in Proc. Zool. Soc. Land., 1891, p. 462, 

 pi. -x.xxvi. See also pp. 258-60 of the present volume and Fig. 7, p. 259. 



