XESTA AND IIELICAKION. 397 



species wMcli live in the islands of the Malayan archipelago are 

 distinguished by their very thick and brilliantly coloured shells. 

 Xesta Gumingii has, on the contrary, a thin transparent shell, 

 which during life is covered by the lobes of the mantle 

 in the same way as the species of Helicarion ; indeed, it is on 

 tlie ground of the form and texture of the shell that it has 

 hitherto been placed in the genus Vitrina. It has, moreover, 

 the long foot which distinguishes Helicarion, and, in fact, I 

 supposed this species to be one of that Philippine genus, until I 

 had examined it anatomically, and so had convinced myself that 

 it belonged to the Indian genus, though it has almost no exter- 

 nal resemblance whatever to the other species. Thus Xesta 

 Cumingii has assumed to a very great extent the appearance of 

 a Helicarion ; moreover, it lives, as I can aver from my own 

 experience, in precisely the same spots as Helicarion, namely on 

 the upper side of leaves in damp woods, and so mixed with that 

 genus that it frequently happened that I captured a specimen 

 of Xesta when I thought I had a species of Helicarion. But 

 it does not possess the power of self -amputation which is charac- 

 teristic of that genus, and hence, when caught by the tail, by a 

 snake or any other creature, it cannot escape in the same 

 manner. 



It follows from all this that we may assume on good grounds 

 that we have here a case of true mimicry — at least it seems 

 hardly possible to think that it is only a singular coincidence. 

 Even Wallace's test and criterion of true mimicry is perfectly 

 applicable here; while the model form (as we may call it) 

 which has a real means of protection is extremely common, the 

 imitating and defenceless form is found in solitary specimens. 

 Hence, the question arises, whether, perhaps, there may not also 

 be in the West Indies land mollusca mimicking the Stenopus — 

 which is provided with the same means of protection as the 

 species of Helicarion in the Philippines — so as to be protected 

 in the same way as Xesta Cumingii. If this should prove to 

 be the case, it would afford, as it seems to me, a strong argument 

 for the accuracy of the view here put forward, that Xesta 

 Cumingii is, in fact, effectually protected by the disguise it has 

 assumed in imitating the species of Helicarion.'^* 



