74 EXPERIMENTAL EVOLUTION LECT. 



are familiar to all. The dwarf rabbits of Porto 

 Santo described by Darwin may also be cited as a 

 case in point Dimensional variations in wild animals 

 are very numerous, and Locard (Etudes sur les Varia- 

 tions malacologiques a" apres la Faime vivante et fossile 

 de la partie centrale du Bassin du Rhone) notes among 

 a large number of similar cases, the fact that many 

 molluscs land or water common to France and 

 Algeria, are much larger in Africa, where their dimen- 

 sions are double those of their European con- 

 geners. 1 Isidore Geoffrey Saint Hilaire says that 

 Lymncea stagnalis is* much larger in ponds than 

 in rivers. Moquin-Tandon notes that in the same' 

 country the same species of molluscs exhibits im- 

 portant dimensional variations, and he has seen 

 Bulimus decollatns nineteen times larger in Africa 

 than in Europe. 



Through careful selection these dimensional varia- 

 tions may become permanent, especially if no change 



1 Such is the case particularly with Helix aspersa, vermiciilata, 

 lactea, melanostoma, Leticochroa candidissima, Fhysa contorta, and 

 many others. And when Leucochroa, for instance, is transferred from 

 Algeria to France it does not acquire a length of more than one centi- 

 metre, while in its African home it is two or three centimetres long. 

 Cf. Locard : L 'Influence des Milieux sur le Developpement des Mol- 

 lusques. Societe d 'Agriculture ', Histoire Naturelle, et Arts Utiles de 

 Lyon, 1891. It has also been issued in pamphlet form by J. B. 

 Bailliere, Paris, 1892. A large amount of facts of French origin are 

 quoted in this valuable contribution to the subject, and the author is 

 one of the leading malacologists. 



