IJfTENSIYE SEGllEGATIOK. 347 



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 branch of the Helieidfe, unlike most other branches, produces 

 its youug, not from eggs, but in a living active form, there is no 

 occasiou in its life-history that requires it to leave the tree in 

 which it lives from generation to generation. In the distribution 

 and divergences of these varieties and species we learn the fol- 

 lowing lessons : — 



1. Varieties are incipient species, and species are strongly pro- 

 nounced varieties. 



A full collection of the varieties and species of any polymorphic 

 genus produces an oppressive sense of confusion on the mind of 

 any one who examines it for the first time. This is preeminently 

 true of a full collection of the AcJiatinelUnce of the island of 

 Oahu. Seven genera or subgenera are represented by a multi- 

 tude of varieties and species, which, within the limits of each 

 genus, are, for the most part, completely 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 varieties 

 that become more divergent as the distance from the home ol 

 the type increases ; and, in the case oi Achatinella and Sulimella, 

 this divergence is so rapid that at the distance of 8 or 10 miles 

 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 

 has changed while the habits remain essentially the same. 



Though it is easy to find degrees of divergence which most 

 naturalists will agree in calling specific, but which in a full col- 

 lection are shown to be completely intergraded, yet if a full col-' 

 Itction of the different 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 



