li FORM-VARIATIONS 93 



very useful, as it can be given as food to animals 

 which will not eat the common spiny form. His first 

 experiments have not proved satisfactory, for the seeds 

 of Ulex nanus have always yielded plants of Ulex 

 europaeus. But since the tendency to vary is strong 

 enough in Ulex europaeus to afford some plants vary- 

 ing in the direction of non-spinosity, we may hope 

 that by means of careful selection Ulex nanus may 

 become an abundant and permanent form. 



So much for integumentary variations. While con- 

 sidering variability of external and superficial charac- 

 ters, we may now say a word of form-variations. 

 These are very frequent among many groups of 

 animals, and particularly among molluscs. Locard, 

 in his interesting and valuable Variations malacolo- 

 giques (vol. ii.), has collected many instances of form- 

 variations noticed by himself and by others. In 

 his opinion, Lymnaa frigida and thermalis are mere 

 varieties of L. peregra, while Ancylus rupicola and 

 thermalis are varieties of A. simplex, the only differ- 

 ence being a matter of mere form. Brot has noticed 

 that in the cool mountain waters, Lymncea auricularia 

 has only four whorls to its shell instead of five, and 

 the Marquis de Folin observes that the pond-snails of 



iCAjonc sans epines, se reproduisant de graines. Bulletin de la 

 Socitte Industrielle d' 'Angers, 1851. Also in Notices sur I' Amelioration 

 des Plantespar le Semis, 1 886. 



