MIMICRY 67 



species of Hclicarion possess the singular property of shaking off 

 the ' tail ' or hinder part of the foot, when seized or irritated. 

 Specimens captured by collectors, Hel. tigrinus amongst them, 

 have succeeded in escaping from the hand, and concealing them- 

 selves, by a sort of convulsive leap, among the dry leaves on the 

 ground. This power of self-amputation must be of great value 

 to Helicarion, not only as enabling it to escape from the clutch 

 of its enemies, but also as tending to discourage them from 

 attempting to capture it at all. Now the genus XeMa is, in 

 anatomy, very far removed from Hclicarion, and the majority of 

 the species are also, as far as the shell is concerned, equally 

 distinct. Xcsta Gumingii, however, has, according to Semper, 

 assumed the appearance of a Helicarion, the thin shell, the long 

 tail, and the mantle lobes reflected over the shell ; but it has not 

 the power of parting with its tail at short notice. It lives 

 associated with Helicarion, and so close is the resemblance between 

 them that, vmtil Semper pointed out its true position, it had 

 always been classified as a member of that group. 



In the same passage Semper draws attention to two other 

 cases of apparent mimicry. The first is another species of Xesta 

 (minclanaensis) which closely resembles a species of Rhysota 

 {Antonii), a genus not indeed so far removed from Xesta as 

 Helicarion, but, as far as the shell is concerned, well distinguished 

 from it. In this case, however, there is no obvious advantage 

 gained by the resemblance, since Rhysota as compared with 

 Xesta is not known to possess any definite point of superiority 

 which it would be worth while to counterfeit. A second case of 

 resemblance between certain species of the genus Chloraea and 

 the characteristic Philippine group Cochlostyla will not hold good 

 as affording evidence of mimicry, for Chloraea is now recognised 

 as a subgenus of Cochlostyla. 



The Mollusca are not much mimicked by creatures of different 

 organisation. This appears at first sight strange, since it might 

 have been thought that tlie strong defensive house of a snail was 

 worth imitating. Still it is probably not easy for creatm-es 

 bilaterally symmetrical to curl themselves up into an elevated 

 spiral for any length of time. One or two instances, however, 

 may be mentioned. The larva of a moth belonging to the 

 Psychidae, and occurring in France, Germany, the Tyrol, and 

 Syria, coils itself up into a sinistral spiral of three whorls, and is 



