LAND MOLLUSKS OF OAHU. 2 13 



Two of these genera, Amastra and Leptachatina, are, for the most 

 part, found under the dead leaves of trees in damp places; and one, 

 Laminella, is found chiefly on low shrubs, while the remaining five 

 genera are always found on trees or shrubs. Now, it must be remem- 

 bered that the climate is tropical, and that the rainfall is so distributed 

 through the year that in the shady groves there is nothing to drive the 

 arboreal species from their haunts on the leaves or branches of the 

 trees. Still further, as this family, unlike most other land mollusks, 

 produces its young, not from eggs, but in a living, active form, there is 

 no occasion in its life history that requires it to leave the tree in which 

 it lives from generation to generation. In the distribution and diver- 

 gence of these varieties and species we learn the following lessons : 



( i ) Varieties are incipient species, and species are strongly pronounced 

 varieties. A full collection of the varieties and species of any poly- 

 morphic genus produces an oppressive sense of confusion on the mind 

 of anyone who examines it for the first time. This is preeminently 

 true of a full collection of the Achatinellidae of the island of Oahu. 

 Eight genera are represented by a multitude of varieties and species 

 which, within the limits of each genus, are, for the most part, com- 

 pletely intergraded with each other. As natural selection has not 

 removed the intermediate forms, it is impossible to say where a species 

 begins and where it ends. Having selected a given form as the type 

 of a given arboreal species, we soon find that it inhabits perhaps only 

 one or two valleys, say half a mile in width, and only one, two, or 

 three miles in length. Beyond these limits it is represented by varie- 

 ties that become more divergent as the distance from the home of the 

 type increases ; and, in the case of the Achatinella and Bulimella, this 

 difference is so great that in districts eight or ten miles apart every 

 one will admit that the forms all belong to different species. Indeed, 

 in many cases, though the same vegetation is present, the habits of 

 feeding have changed, while in other cases the form and color have 

 changed while the habits remain essentially the same. 



Though it is easy to find degrees of divergence which most natu- 

 ralists will agree in calling specific, but which in a full collection are 

 shown to be completely intergraded, yet if a full collection of the dif- 

 ferent forms should be submitted in succession to a hundred different 

 naturalists to classify, it would be found that no two would agree as 

 to the number of species, and a still greater diversity of opinion would 

 be revealed as to where the limits of the different species should 

 be placed. This is exactly what we might expect if varieties are 

 incipient species, and species are simply strongly developed varieties. 

 Such being the case, it is folly to ask that the nomenclature should 



