MEANINfi OF SHAPES AXD COLOURS OF THE MEMBRACID^. 5 



together : in the Memhracidce the disguise is chiefly borne and often solely borne by 

 the pronotiim alone. The marked reseml)lance to ants in the genus IL'feruiiofus, the 

 strange and remarkable shapes which we should probably recognise as cryptic if we 

 saw the living insects in their natural environment — these are borne by a mask which 

 is a development from a relatively small part of the organism. The Membracid, 

 as a whole, bears not the slightest resemblance to ant or thorn or bark, but it is 

 covered by a shield which does bear a striking resemblance in some species to the 

 first, in others to the second, in others again to the third, of these objects. 



Those who oppose the interpretation based on natural selection are therefore faced 

 by the question — how, except by selection, can it be conceived that the variations of 

 shape in the prouotal shield of an insect can have been guided into the superficial 

 resemblance to an ant, while variations in the whole body-form of another have 

 assumed the same appearance, while in a third the likeness is indicated by colour 

 alone, resulting in the invisibility of those parts which would interfere with the 

 resemblance ? The attainment of the same end by entirely different means affords 

 strong support to the opinion that the end is advantageous. On any other hypothesis 

 as yet put forward it is a meaningless coincidence that the model suggested in each of 

 these three different wa3'S, is the same specially aggressive and well-known insect. 

 This argument was first suggested by the present writer at the Toi'onto meeting of 

 the British Association in 1897 (lleport of the Meeting, page 692) and was further 

 developed with the aid of illustrations in the Journal of the Lijii/enn Society (Zoology, 

 Vol. XXVL, pp. 588-595). 



In the following pages I have employed the word " mimicry " to indicate re- 

 semblances to other species of animals. Likeness to plant structui-es, &c., for the 

 purpose of concealment I have invariably called "cryptic" or "protective re- 

 semblance." Among the Membraddce such concealment is always "procryptic," for 

 the purpose of defence ; although antici-yptic or aggressive resemblances to plants are 

 well known in insects, especially in the flower- and leaf-like mantides (seepage 153). 



In discussing the effect of hereditary bias towards particular colouring (see page 

 200) I was considering only the cases of insects in which each individual possesses a 

 power of special adjustment to two or more of its possible environments. For 

 example the larvae of the moth Amphidasis betularia have the power of becoming black 

 on a plant with black twigs, green when the tv.'igs are green, white when they are 

 glaucous, &c. {Trans. Eni. Soc. Lond., 1892, pp. 326-360). This individual adapta- 

 bility and freedom from bias is clearly advantageous. If, for example, the effect of 

 green shoots persisted in the next generation it would be injurious to the great 

 majority of the larvtc, for the parent moth generally lays her eggs on plants with 

 dark twigs. The same argument applies to the smaller difterences Avhich distinguish 



