293 



A CROSS BETWEEN TYPICAL HELIX ASPERSA AND 

 VAR. EXALBIDA: ITS RESULTS AND LESSONS. 



By a. W. STELFOX, M.R.I. A. 



(Read before the Society, Jan. 13th, 1915). 



Before conchologists became acquainted with the results of 

 Mendel's experiments, several attempts were made to procure 

 specimens of sinistral shells and other extreme variations by crossing 

 one of these with a typical example of the same species. Un- 

 fortunately through lack of knowledge these experiments were 

 only carried to the F i generation, in which the aberrant form — 

 being recessive — could not appear. Hence many naturalists came 

 to believe that such forms were " freaks " incapable of transmitting 

 their characteristics to their descendants. I remember well being 

 told by a former president of our Society that the colony of white 

 Clausilia bidetitata at Kinbane, co. Antrim, could not be due in any 

 way to heredity. I had been reproving him for collecting all the 

 white shells, by suggesting that this might exterminate the colony ; 

 but at the time I was quite satisfied with his answer. I know now 

 that he was entirely in the wrong. 



Upon finding a specimen of Helix aspersa var. exalbida near 

 Dorking, Surrey, in September 191 1, I determined to keep it for 

 experimental purposes. During the following month it was placed 

 in a box with a more or less typical example taken at Carrickfergus, 

 CO. Antrim, in August 19 10. Throughout the following experiment 

 the snails were fed on lettuce leaves and slices of carrot or turnip. 



In February, 19 12, both specimens came out of hibernation and 

 were observed to pair on the following day. No eggs were laid ; 

 but they again paired several times and eggs were laid in a burrow 

 in the sand at the bottom of the box during May. By which 

 specimen the eggs were laid I do not know. On the 25th June 

 and following days the young were hatched. They grew quickly 

 and by Xmas 19 12 some had reached a diameter of 15mm. • the 

 smallest being about 9mm. in diameter. All hibernated during the 

 winter, most by fastening themselves against the side of the box ; 

 some buried themselves in the sand with the mouth of the shell 

 upwards. I was interested to discover the means by which these 

 burrows are excavated ; it is, I believe, by using the foot-sole as a 

 "conveyor." First a sort of round depression is made with the 

 head ; and then the snail proceeds to walk into the sand. The 

 shell coming in contact with the sand hinders movement, and con- 

 sequently it is the sand under the snail that travels, being thrown 



