268 



RESEARCHES INTO THE HEREDITARY CHARACTERS 

 OF SOME OF OUR BRITISH MOLLUSCA. 



Part II. 



Helix aspersa Miill. and H. nemoralis L 



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



(Read before the Society, June 13th, 1917). 



Under this title I propose to lay before the Society the results of my 

 breeding experiments, from time to time, as may seem desirable. 

 Some of these have now been carried through four generations and 

 their commencement dates back to the years 1909, 1910 or 1911. 

 Until the present most of my experiments have been more or less of 

 a preliminary nature, at first at random, afterwards with the definite 

 object of obtaining pure races of certain well-marked varieties for the 

 purpose of intercrossing. During these preliminaries several interest- 

 ing facts have come to light, which I think it may be well to place on 

 record, and which I hope will prove of general interest. 



In the first case I shall proceed further with my Helix aspersa 

 experiment, referring to it and subsequent ones under the numbers 

 used in keeping my records. 



Experiment No. 25. Helix aspersa Miiller. 

 The ^first part of this experiment has been laid before the Society 

 already, carrying it on to the F2 generation, in which there appeared 

 72 examples of var. exalbida out of a total of 311, the remainder — 

 239 — being typically coloured. Two of the young exalbida were 

 isolated and reached full growth towards the close of the summer of 

 1915, but eggs were not laid until the following year, and the first of 

 the F3 generation did not hatch out until the 4th of September, 191 6. 

 Two distinct batches of young appeared, no doubt from eggs laid by 

 both parents, numbering in all well over 100 individuals, all of which 

 from the first were at once identifiable as exalbida. Further research 

 has tended to prove, therefore, that my former surmise was correct, 

 namely, that the var. exalbida is a homozygous recessive form of the 

 species. If this be true, any two exalbida will if crossed produce 

 exalbida only, akvays provided that neither has been already fertilized 

 by a typically brown specimen. 



ExPERiiMENT No. 1. HcHx ncmoralis L. 

 In March, 1910, four specimens from the precincts of Cross Abbey, 

 near BelmuUet, in West Mayo, were placed in a box together. All 



I A cross ' between typical Helix aspersa and var. 'exalbida, Joiirn. of Conch., vol. x\v., 

 pp. 293— 295, 1915. . ..... .. ...... 



