130 THE TRANSFORMATIONS OF THE ANIMAL WORLD 



Coutagne was in this manner enabled to establish 

 that different colonies had often each a sort of 

 special physiognomy manifesting itself by charac- 

 teristics difficult to clearly define, such as colour 

 of the epidermis, thickness of the test, relative 

 size of the shell, etc. In addition, it is often ob- 

 served that these same characteristics are again 

 met with in other species from the same locality, 

 so that their production may reasonably be at- 

 tributed to the influence of the environment. We 

 arrive, it will be seen, by a stricter and more exact 

 method, at the distinction pointed out above be- 

 tween variations produced on the spot or varieties, 

 and variations at a distance or local races. 



Coutagne has contrived to systematize with pre- 

 cision the various modes by which these variations 

 in land shells are effected. He observes first of 

 all that certain species, the Helix lapicida, for 

 instance, have almost no polymorphism. Doubtless 

 certain individuals are a little flatter, others, on 

 the contrary, have a higher spiral : the carina is 

 more or less sharp, the umbilic more or less open. 

 But all these variations alter so slightly the physiog- 

 nomy of the shell, or, if preferred, the characters 

 of the species, that the least expert conchologists 

 will never hesitate, after they have once seen this 

 species, to recognize it among all these slightly 

 differing varieties. 



Other species, on the other hand, are more poly- 

 morphous. It might almost be laid down as a 

 rule that the variability of a Linnaean species may 

 be in some sort measured by the number of forms 

 or so-called species into which it has been dis- 



