XXVI THE SPECIES CONCEPTION. 



occupying the same area without intergrading or hybrid 

 forms. 



Races included under (II) may be illustrated by the group 

 composed of Achatinella phceozona, fulgens, stewartii and 

 vulpina. By reference to the map on p. 183, it will be seen 

 that the areas of these overlap slightly, but are in the main 

 separate. At the points of contact there are transitional 

 colonies which have every appearance of being hybrid groups, 

 composed of individuals having various combinations of the 

 characters of the adjacent races. It will readily be seen that 

 the "species' of this grade do not have the same value as 

 those of grade I, and they might be more logically considered 

 subspecies. Such treatment of the section Achatinellastrum 

 would reduce the species from 17 to 10, as explained on p. 181. 

 In the genus Achatinella it has been thought more practical 

 to recognize as "species' a certain number of races which 

 admittedly intergrade at their limits, than to make the species 

 conception so broad that no definite idea is conveyed. More- 

 over, the term subspecies is needed for subdivisions of lower 

 grade. Thus the Koolau forms of A. fulgens show slight 

 racial divergence, which is recognized by the term A. fulgens 

 versipellis. 



In Achatinellastrum and Bulimella, then, it is frankly ad- 

 mitted that the species of this work are groups of two grades, 

 certainly differing widely in degree, quite likely differing in 

 kind. Related forms which inhabit the same district without 

 evidence of hybridizing may safely be put down as species 

 of the first grade. In other forms, which may appear equally 

 as distinct phenotypically, we find abundant evidence of 

 hybridizing where their areas overlap ; and these we rank as 

 species of the second grade. How fundamental this distinc- 

 tion is in animals generally we do not know, and it has not 

 yet been satisfactorily worked out from the experimental side. 

 Practically the grade of any given form is to be decided in 

 each case by field observations and abundant collections. On 

 pages 119 and 181 the real or first grade species of Bulimella 

 and Achatinellastrum are indicated. In the section Acha- 

 tinella s. str. ("Apex"), the conditions are very complex. 



