VARIETIES OF THE FIELD-SNAIL (Helix hortensis) 



Variation is one of the fundamental phenomena upon which the 

 Evolution Theory is based. No two individuals of the same 

 species are ever precisely alike, a fact familiarly illustrated by 

 the dissimilarity which often exists between children of the same 

 parents. It appears that all parts of the body are liable to varia- 

 tion, which may be of very marked kind and is no doubt, at least 

 in part, due to the action of surroundings. A typical cas, selected 

 for this plate because it appeals to the eye, is that of the Field- 

 Snail (Helix hortensis), of wrjich some 90 races or varieties have 

 been described. In some of these the shell is "self-coloured", 

 yellow or pinkish-brown being common tints. In other cases there 

 are in addition dark bands, the number of which is distinctive 

 of the race, while the ground colour has also to be considered. 

 Enough varieties have been introduced into the plate to illustrate 

 the principle. 



