128 PEARCE : VARIETIES OF BANDED SNAILS. 



shape of shell in this particular species, it is found on the turf 

 and grass of our downs, heaths, and sheep pastures. 



And how is it possible to attempt to answer the question 

 as to the cause of these various markings and bandings in 

 Helix caperata? How, for instance, may we seek to explain the 

 association together on our downs of two varieties with such 

 distinct markings as those of the variety ornata and the mottled 

 forms we have just referred to? If the markings mean anything 

 we cannot but suppose that there is an advantage in the one class 

 of marking over the other which meets some special circum- 

 stance or need in the life of the mollusc. 



Now I have been brought gradually to think that the sheep 

 that browse on our open downs and pastures have been the 

 chief, if not the sole, means by which the variety has been 

 evolved from the mottled form. One was first led to consider 

 this a probability from noticing that the var. ornata is practi- 

 cally restricted to localities where sheep are pastured with fre- 

 quency; while in the localities where sheep never feed — such as 

 sand-hills by the sea, or rocky broken ground, and other places 

 impracticable as sheep-pastures — the mottled variation is seen to 

 be universal, though just now and then, very unfrequentl}', one 

 or two individuals of the variety ornata may turn up, as if to 

 remind us that there is such a variety in existence. 



To briefly put into a tabular form the sum of our evidence 

 gathered together in support of the above proposition, we find 

 the proportion in which the two varieties of Helix caperata occur 

 in sheep pastures is as under : — 



PLACE. VAR. ornata. mottled var. 



Isle of Wight Downs, Sept., 1887 



Cow Gap, Eastbourne, Jan. 18S8 



Ditto Sept., 1888 



Beachy Head, near Eastbourne, 

 Aug., 1888 



Totals 



