52 ELEMENTS OF BIOLOGY. 



ters of other species, to which they may be closely related, 

 or from which they may be very widely removed in their 

 zoological position. Such cases are said to be examples of 

 "mimicry," and such animals are said to be "mimetic." 

 One of the best examples which can be given of this, is the 

 resemblance which certain of the South American Butter- 

 flies exhibit to the Helico7iid(E^ a very brightly-coloured and 

 well-marked group of the butterflies of the same country. 

 Certain of the South American butterflies which are in no 

 way allied to the Jfenco7tidce, and which are also not related 

 to each other, very closely simulate the colours and mark- 

 ings of the Heliconidce. ; and no doubt can be entertained 

 but that this '' mimicry" is serviceable to the mimics and 

 protects them from injury. Mr Bates, in fact, who dis- 

 covered the above facts, asserts that the Heliconidce^ though 

 very numerous and gaudy in their colouring, are not liable 

 to be attacked by other animals, probably in consequence 

 of their possessing a strongly offensive odour. The mimic- 

 ing butterflies, of course, do not acquire this odour, but 

 they are liable at a distance to be mistaken for the distaste- 

 ful HelicojiidcB, and are thus doubtless greatly protected from 

 the attacks of birds. Many other cases of this kind of 

 mimicry are known, and it would seem that in all such cases 

 the mimetic species is protected from some enemy by its 

 outward resemblance to the form which it mimics. 



In another extensive group of cases, we find an animal 

 imitating, not some other animal, but some natural object, 

 and thus greatly reducing its chances of being detected by 

 its natural enemies. Admirable examples of this are afforded 

 by the insects known as Spectres {Phasmidce)^ some of 

 which imitate dried twigs, and are called walking-sticks, 

 whilst others closely resemble leaves, and are known as 

 walking-leaves (fig. i8). The advantages gained in these 

 cases are extremely obvious, the insect being plainly pro- 

 tected from its foes by its resemblance to such an object as 

 a piece of dead wood or a fallen leaf The closeness of the 



