128 PROBLEMS OF GENETICS 



midata. In France generally they are distinct enough from 

 each other, trochoides being smaller and having a characteristic 

 keel. Coutagne says that after having collected these species 

 from more than a score of localities he came upon a colony of 

 trochoides on the island of Pomegues in which the shells were 

 relatively enormous, most of them having only a slight keel, 

 and a few none at all. On the other hand he received a con- 

 signment of pyramidata from four localities in Sicily, all small, 

 and one of them exactly like the trochoides from Pomegues. 

 Judging by the samples received from Sicily, trochoides is there 

 not more variable than it is in Provence, while the Sicilian 

 pyramidata is protean. 



The relations of the two species Helix nemoralis and hortensis 

 provide an illustration of another kind of manifestation of local 

 peculiarity. H. hortensis and nemoralis as usually met with, 

 are two very distinct forms. H. hortensis is smaller and duller, 

 and its peristome is white. H. nemoralis is larger and more shiny, 

 and its peristome is brown. In several anatomical points, 

 moreover, especially in the shape of the dart, there are great 

 differences. For a full account of these peculiarities of the two 

 forms and a discussion of their inter-relations the reader is re- 

 ferred to the elaborate work of A. Lang 14 who has studied them 

 extensively and has also succeeded in experimentally raising 

 hybrids between them. These hybrids were in a slight degree 

 fertile with both the parent species, but up to the time of pub- 

 lication no young had been reared from hybrids inter se. 



Coutagne describes the result of collections made in 62 

 French localities. Some had exclusively hortensis, some ex- 

 clusively nemoralis, and in some the two were found in associ- 

 ation. He gives details of five of these collections from which I 

 take the following summary of the more essential facts, omitting 

 much that is almost equally significant. 



Locality A , near Honfleur. Both forms present, each sharply 

 and normally distinguished, without any intermediates. They 



14 A. Lang, Die Bastarde von H. hortensis Mutter H. nemoralis L. Jena, G. 

 Fischer, 1908; with a fine coloured plate showing the varieties of the species and 

 their hybrids. 



