VARIATION AND LOCALITY 125 



Somewhat comparable variability has been seen in another 

 Orchid genus Ophrys. In Great Britain the species apifera, 

 aranifera and muscifera though variable are fairly distinct, but 

 Moggridge has published two series of plates 10 showing a very 

 different state of things as regards the Ophrys population of the 

 Riviera. Here the outward diversity is such that the ordinary 

 specific names cannot be applied with any confidence and the 

 limits of the species are quite uncertain. It may well be supposed 

 that these Riviera plants are interbreeding, and indeed we may 

 safely assume that they are. It is, however, to be remembered 

 that Darwin showed apifera in this country to be habitually self- 

 fertilised, so that the different behaviour on the Riviera may 

 itself constitute a local peculiarity. Moreover it is to be gathered 

 from Moggridge's account that in the districts which he examined 

 the condition was not to be described by the statement that our 

 three types were there co-existing and hybridising, but rather 

 we should say that the population was polymorphic, containing 

 these three types amongst others. Conchologists are aware 

 that on the Dogger Bank Modiola attains a size unparalleled 

 elsewhere. The same is true of the sponges Grantia compressa 

 and Grantia ciliata in the estuary of the Orwell. 11 Conversely, 

 as we know so well in the case of Man, dwarf races occur in 

 several special localities. Such examples may be multiplied 

 indefinitely. 



The relation of local forms to species has often been dis- 

 cussed from many points of view, but I know no treatment of 

 the subject clearer or more comprehensive than an excellent 

 account of some of the various manifestations of local dif- 

 ferentiation as they appear in Helicidae published by Coutagne 12 

 and a reader interested in the problem which they raise would 



10 Flora of Mentone, 1864-8, Nova Acta Acad. Caes., XXXV, 1869. 



11 I owe these facts to Canon A. M. Norman, who showed me illustrative 

 specimens. They were originally described by Bowerbank (Monogr. Brit. Spongi- 

 adae, vol. II, pp. 18 and XX; vol. Ill, Pis. I and III). A specimen of G. compressa 

 measured 5 inches, with a greatest width of 3 x /i in. G. ciliata was found measuring 

 3 in. long and % in. wide. These dimensions are many times those of normal 

 specimens. 



12 Coutagne, G., Recherches sur le Polymorphisme des Mollusques de France 

 Annates Soc. d'Agric. Sci. et Industr. Lyon, 1895. 



