6 MEANING OF SHAPES AND COLOURS OF THE MEMBBACIDJ^. 



the dark twigs of various trees from each other ; for these also are reproduced upon 

 the larvae. Thus Mr. Arthur Sidgwick has shown tliat the caterpillars, when found 

 upon birch and oak, differ, as do the dark twigs of these two trees (I.e. p. 360). It 

 has not yet been shown that any Menibracid has this jwwer of adjusting its colour 

 to two or more environments, so that my argument does not at present apply to 

 these insects. If, however, it is at all possible to breed them it would be deeply 

 interesting to ascertain whether any such adaptability exists. The best chance of 

 success would be afforded by experiments upon well-concealed species of which the 

 individuals are known to vary greatly, but always in the direction of some one of 

 their natural environments. 



It is now proposed to make a brief survey of the material illustrated in this 

 monograph and to attempt to suggest the possible bionomic meaning of the appearances 

 into which the enveloping pronotal shield is fashioned in the various groups of 

 species. 



Commencing with the sub-family Memhracincp, the genus Moiibracis includes the 

 species with the pronotum high and compressed from side to side, and coming to a 

 sharp thin edge like a leaf. Beneath this leaf-shaped structure, which is dark, 

 mottled with white or yellow, the head, wings, and legs of the insect are seen (see 

 Plates I. and II.). Inhabiting the same part of the world, tropical America, in 

 which alone this genus is found, are ants of the genus QScodoma (Sauba ants). The 

 ants live upon fungi which they cultivate in galleries underground, growing them 

 upon a paste of bitten-up leaves. To provide this soil streams of ants are continually 

 passing to the formicarium, each bearing a piece of leaf held vertically in its mandibles 

 and thrown back over the body. The ants are extremely common, so much so 

 indeed that certain kinds of imported trees cannot live in that part of the world, and 

 the processions of leaf-carriers as well as the single ants are among the most familiar 

 and characteristic of sights. The Memhracida on the other hand are scarce. Green 

 leaves are not the only things sought out by the ants ; they have been seen carrying 

 oft parts of the wings of butterflies, as well as leaves discoloured in various ways. 



It seems possible that the rare Menibracis with its high laminar pronotum may 

 pass undetected among the numerous leaf-carrying ants which are partially concealed 

 beneath their burdens in much the same manner. Furthermore the pronotum is 

 about the same size as the fragment of leaf and the Membracid as some of the 

 forms of the worker ants. 



I do not desire to press this interpretation with confidence, but merely bring it 

 forward as a suggestion. I venture to hope that naturalists visiting tropical America 

 will observe whether the leaves carried by the ants do not sometimes possess the 

 curious parti-coloured appearance of the Membracid pronotum. 



