594 PEOF. E. B. POTJLTOM" : NATURAL SELECTIOIS' 



This change has been brought about, and certain species of t'le 

 group have their un-ant-like bodies concealed under an ant-like 

 shield. In other species the prothoracic shield is modified into a 

 resemblance to other objects, such as seeds, thorns, &c. — an 

 excellent example of the parallelism between mimetic and pro- 

 tective resemblance insisted on on page 565. The effects pro- 

 duced in the shield are at least as exact and detailed as those 

 which in other cases are wrought in the form of the whole 

 body ; for, as Mr. W. P. H. Blandford lias pointed out to me, a 

 peculiar characteristic of certain tropical American ants (viz. the 

 bead-like dilatation in the stalk of the abdomen) is reproduced 

 in the shield of the membracid. This is well seen in Heteronotus 

 trinodosus shown in fig. 6, copied from Canon W. W. Powler's 

 Monograph of the group in the ' Biologia Centrali-Americana.' 



Finally, in the same group of Memhracidts we meet with another 

 example which is also incapable of interpretation by any theory 

 as yet brought forward except natural selection. An immature 

 form of membracid, with the prothoracic shield not yet formed, 

 found by "W. L. Sclater in British Guiana, strongly resembles 

 one of the leaf-carrying ants which are so common in that part 

 of the world ; but the resemblance includes the leaf as well as 



Fig. 7. 



Fig. 7. — About three times the natural size. On the right is represented an 

 immature Membracid (Rhynchota Homoptera) from British Guiana, 

 which resembles an ant together with the leaf it i.s carrying. The 

 latter is shown on the left, and represents the species Q^codoma cepha- 

 lotes from the same locality. (From Poulton, Proc. Zool. Soc. 1891, 

 pi. xxxvi. fig. 2.) 



the ant ! The dorsal region of the membracid is flat and 

 compressed, so that it is as thin as a leaf; its border (the dorsal 

 surface, which formed a sharp edge) is jagged like a gnawed leaf, 

 and during life it was green in colour. Beneath this leaf-like 



