114 Taylor: Xotex on Sinfs/ni/ Shells of Liniticea peregra. 



Although none but tlie sinistral varieties were in the 

 aquarium, nearly equal numbers of sinistral and dextral were 

 produced, the sinistral slightly preponderating. They all grew 

 to the usual size of the species and having come to the ful- 

 ness of maturity, died. 



The water in the pond is quite as pure as in similar ponds 

 and the shells are not malformed. A pond about 12 feet 

 away and separated only by a hedge contains none of them. 



The other molluscan inhabitants of the pond are quite 

 normal, including fine specimens of the type species : Pisidium 

 fontinale in the mud, and the very small Planorbis nautileiis 

 living on the undersides of the duckweeds {Le?)ina muior). 



The shell has not occurred in any of the other ponds in 

 the neighbourhood, and the above facts I think are of interest in 

 showing the persistence of the monstrosity. 



NOTES ON SINISTRAL SHELLS OF 

 LIMN/EA PEREGRA. 



J. VV. TAYLOR. 

 Leeds. 



The persistent occurence of this phenomenon, for so long a time 

 within such a very limited area, strongly corroborates the belief 

 that local environment is one of the contributory causes inducing 

 this condition of shell and animal. 



All embryonic gastropods are at first, what is termed Kxo- 

 gastric, that is, they have the spiral enrolled to the front and 

 the excretory and other orifices behind, and whether the animal 

 becomes sinistral or dextral depends on whether the twisting, 

 which the body subsequently undergoes, takes place to the right 

 or to the left, this movement transferring the anal and other 

 orifices from the hinder part of the body to the front. 



The cause of this reversal of the normal coiling- is not under- 

 stood, Bourguignat suggested that it might be caused by 

 electrical conditions, while Prof. Carus believes that the direction 

 of the coiling may be determined by the direction of the embry- 

 onal rotation. 



The results of the breeding of sinistral specimens of Linnucu 

 percgra by Mr. Trechmann establishes the inheritable nature 

 of the variation and the relative number or proportion of sinistral 



Naturalist, 



