396 THE INFLUENCE 0V LIVING SURROU]S 7 DINGS. 



spring into the air, so that it falls over on to the ground. 

 These snails at first constantly escaped me and my collectors in 

 this way, and not unfrequently we had nothing but the tail left 

 in our hand. According to Guilding's observations the same 

 peculiarity of parting with the hinder prolongation of the foot 

 characterises the West Indian snail Stenopus. I ascertained by 

 further investigation that in a free state of nature such self- 

 mutilation not unfrequently occurs, for out of about a hundred 

 specimens of Helicarion gulla, which is extremely common in 

 the north-east of Luzon, I found perhaps ten individuals that 

 had shed their tails, or, to speak more accurately, the hinder end 

 of the foot, and had the stumps partly healed, or the foot to 

 some extent grown again. Now, this hinder portion of the foot 

 is the most conspicuous part of the snail's body, and it may be 

 supposed that it is, in most cases, the part first seized by the 

 reptiles or birds that prey upon them ; but, startled by the 

 escape of the body itself, they would soon learn to recognise, by 

 the form of the tail, those species which were capable, by this 

 self-amputation, of depriving them of the larger and probably 

 the only valuable portion of the prey. In this way the species 

 of the genus Helicarion can escape the pursuit of their enemies 

 better than they otherwise could on account of their exposed 

 mode of life, and it is in agreement with this fact that, in the 

 spots where they occur, they are commonly to be found in 

 numbers together. But other land-snails which are not in fact 

 protected by any such peculiarity might very well be equally 

 effectually protected by mimicry of the appearance of a Heli- 

 carion, since they might thus be mistaken for them. 



One single species of snail does, in fact, exist in the Philip- 

 pines which actually bears an extraordinary resemblance to the 

 species of Helicarion, although in internal structure it is, syste- 

 matically speaking, very far removed from it, and does not even 

 belong to any of the genera which are characteristic of these 

 islands ; this is Vitrina Cumingii, a species long since known as 

 having been discovered by Chiming in Mindanao (see fig. 105, d). 

 An examination of the living animal convinced me that it 

 belonged neither to Vitrina nor to Helicarion, but to a 

 thoroughly Indian genus, Xesta, of which the very numerous 



