5O ENTOMOLOGICAL NEWS [Feb., ? 2O 



arbitrarily, or if you prefer, with discretion. It has been a 

 guide not the commander of the advance. 



Carried out logically, recognition in taxonomy of the prin- 

 ciple of intergradation decides another much debated point 

 the status of island races, or even of those inhabiting separate 

 continents. If individual variations are such that overlap- 

 ping of all the differential characters occurs, the forms should 

 be regarded as subspecies; if not, they are properly considered 

 as species. These conclusions, also, are not universally ac- 

 cepted. To some naturalists, obvious isolation as of island 

 forms, and real or assumed isolation of continental races, 

 apparently is taken as proof of specific distinctness. For the 

 purpose of throwing light on this view we may consider the 

 case of certain birds of the perennially interesting Galapagos 

 Islands. Within the limits of a single and' evidently very 

 plastic genus Geospiza there are species confined to a single 

 island, or to two islands, and so on, up to II islands in the 

 highest number recorded by Snodgrass and Heller.* What 

 is a more cogent argument in the case, there are also subspecies 

 that occur in just the same way, some of them upon only a 

 single island, others upon two or more up to a maximum of 

 eleven. Here is definite proof drawn from forms wholly of 

 one highly plastic genus that a single subspecies actually 

 ranges throughout a considerable number of well-separated 

 islands, to certain of which at the same time, other subspecies 

 and even species, among its congeners, are entirely restricted. 

 In other words, the case proves, that isolation in itself is not 

 admisssible as a decisive factor in giving specific rank to or- 

 ganisms. 



If such is the case when the isolation is that of islands 

 separated by stretches of water in some instances of consider- 

 able width; if such isolation is not accurately reflected in the 

 relationships of the animal inhabitants, what weight can be 

 given to alleged cases of isolation on continental areas, where 

 knowledge that the isolation is real, is difficult if not impos- 

 sible, to obtain? 



*Proc. Wash. Ac. Sci. Vol. 5, pp. 231-372, January, 1904. 



