400 THE INFLUENCE OF LIVING SURROUNDINGS. 



pai't of the island of Luzon ; not a single species of Chlorcea is 

 found in Mindanao, and only one of Dorcasia. Now, the anato- 

 mical investigation of several species of both groups (see fig. 73) 

 has proved that they are very nearly allied to each other, and, 

 at the same time, to one of our commonest European land- 

 snails, Helix fruticum. But as regards their shells they differ 

 so widely that in systematic classification Chlorcea is placed far 

 from Dorcasia, and also from Fruticum. The shell of Dorcasia, 

 however, is easily recognised as allied to Fruticum from its 

 resemblance to that type in colour, form, and marking, so that 

 it is to me quite incomprehensible why conchologists should 

 hitherto have disregarded so striking a similarity in the shells. 

 On the other hand, all the shells of the group of Chlorcea so 

 singularly resemble those of Cochlostyla, of which the animals 

 follow the same mode of life as the species of Chlorcea, that they 

 have hitherto been generally regarded as species of the Philip- 

 pine genus, and in many of the species it is, in fact, quite impos- 

 sible to decide which they belong to, so long as the shells alone 

 are compared. Thus, on one side, a few species have preserved 

 their resemblance to Fruticum, and with that the same mode of 

 life; and on the other, a few have assumed the aspect of another 

 genus and live on trees associated with certain species of it. 

 Hence Helix fruticum ought properly to be included in one 

 genus with Chlorcea and Dorcasia, and thus combined they 

 would be closely connected with the genus Cochlostyla. Sup- 

 posing now that a form represented by Helix fruticum were the 

 original form as there are various reasons for supposing 

 some few species of that genus, when they migrated into the 

 Philippines, would have preserved their original external appear- 

 ance and at the same time their old habits of life; while others, 

 acquiring the habit of climbing trees, would have become so 

 much modified in form, colouring, and sculptured marking, that 

 the closest scrutiny of the shells alone would not suffice to 

 decide the question whether they belonged to Cochlostyla or 

 not. We might then easily be tempted to attribute this simi- 

 larity to a process of protective mimicry ; but such an assumption 

 would be at once contradicted by the fact that the species of 

 Chlorcea: and Cochlostyla which most resemble each other, do 



