162 PARTULA. 



Most species of Partula are neither more nor less variable 

 than the generality of snails living in exposed situations 

 elsewhere. It is only in the Society Islands that species oc- 

 cur having a variety of well-developed color-patterns. In this 

 respect they resemble many other genera of arboreal snails, 

 such as Amphidromus, Liguus, Hemitrochus, Polymita, 

 Drymceus etc., etc. All arboreal snails were derived from 

 terrestrial forms ; and almost invariably, with arboreal habits 

 they assume variegated color-patterns. In many cases the 

 colors or patterns seem to be protective (cryptic or warning), 

 but as often they are not so, to our eyes. The color-patterns 

 in arboreal snails seem to be very readily modified, new 

 sports or mutations arising, which are perpetuated, prob- 

 ably in Mendelian ratio, in the parent colonies. This has 

 not yet been tested experimentally in Partula ; yet from the 

 complex nature of many colonies,, in which snails of several 

 distinct color-patterns co-exist and interbreed (being found 

 together in the uterus of a single mother) , I have little doubt 

 that pedigree cultures would reveal a Mendelian mixture. 



Another 'Common 'condition among tree-snails is the sim- 

 plification or absence of pattern, by variation in the "color- 

 factor/ 7 whereby patterns characteristic of species or phyla 

 become in part or entirely latent in individuals or races. 

 Cf. the Pentatceniate snails, Drymczus, Amphidromus etc. 

 Some species of Partula, such as P. hyalina, are apparently 

 albinistic; but in at least a part of these (P. arguta) the 

 mantle is variegated, showing through the transparent shell, 

 which in life should vicariously show a pattern. 



Probably most "species" of snails and other sedentary 

 animals are in reality more or less complex groups, though 

 in plain-colored forms their composite constitution is not 

 obvious. In some of the plain, ground-living American snails, 

 such as Omphalina, the diversity in number of teeth of the 

 radula among different colonies points to this conclusion. 



In the Society Islands, where alone the distribution of 

 Partula has been studied, most species and races are strictly 

 limited to small areas, a single valley, or several 'contiguous 



