55 

 SINISTRAL LIMN^A PEREGER Miill. AND ITS PROGENY. 



By J. A. HARGREAVES. 



(Read before the Society, September 13th, I9i6j. 



For fifteen years a pond near Leeds has been known to yield 

 occasional sinistral specimens of L. pereger. As far as I have been 

 able to learn they have occurred with fair regularity through successive 

 seasons, though probably more abundant at one time than another. 

 1 am inclined to think that in 1916 they were unusually common, as 

 in several visits my friends and I got a fair series. 



In addition to L. pereger the following species occur in the pond: — 

 Vivipara vivipara - - common 

 Planorbis corneus - - common and large 



P. umbilicatus - - common 



P. albus . - - - rather scarce 

 Limncta stagnalis - - common 



SphcBrmm cortieitvi - - common 



I have not obtained sinistral forms of any species except Z. pereger, 

 nor can I ascertain that any have ever been found there. 



I thought it would be a useful experiment to hatch out several 

 series of eggs from both sinistral and dextral parents and tabulate 

 accurately the results. 



One serious drawback to the experiment was that the character of 

 only one parent was known. In two or three cases specimens were 

 taken in copula, but always with a dextral mate, whilst the fact that 

 in the pond itself probably over one per cent, and under two per cent, 

 of the L. pereger ai-e sinistral shows that in the great majority of cases 

 one parent would necessarily be dextral. It is, however, quite 

 possible that in some cases both parents might be sinistral. When 

 the Limncea were obtained, the sinistral specimens were at once iso- 

 lated in a separate jar. Several soon deposited eggs on the Elodea 

 canadensis which was placed in the jar with them, and which was 

 obtained from the same pond. The Elodea was most carefully 

 scrutinised, to be certain that there were no eggs on it, before it was 

 placed in the jar. 



The batches of eggs as laid were placed in separate glass jars or 

 saucers to hatch. A second drawback to the experiment was that the 

 jars had to be left unattended, some in Leeds, some in Scarborough, 

 for several days at a time. Possibly this affected the numbers of 

 young hatched, as the water was not changed so frequently as 

 desirable, and in such small receptacles it is apt to become foul. The 



