344 Mr, P. R. Lowe on Coloration as a Factor in 



on the subject of species and their distribution. I have 

 recently spent a considerable time over this group, chiefly 

 from the point of view of colour-pattern, and ray conclusion 

 derived from this source is — that not only is there but one 

 genus, as is maintained by Messrs. Rothschild & Hartert, but 

 that there are but three or four species, instead of 35, and 

 that these species were polymorphic. One of tlie things I did 

 was to segregate all the examples of the ten Duncan Island 

 species into one box, and then examine them from the point 

 of view of intergradations in the form of the bill and 

 colour-pattern. It was an interesting experiment, and, as 

 I say, the only conclusion one could come to was the poly- 

 morphic nature of the two or three species, although it is 

 conceivable that one or two forms may become, or are 

 becoming, dominant, and may eventually become fixed. 



I have instanced this case of the genus Geospiza because 

 of the perfect series of intergradations in the form of the 

 hill which are alleged, and because from that fact the 

 common-sense view seems to be that we are here justified in 

 lumping. On the other hand, here are three Icterine genera, 

 Trupialls, Leistes, and Sturnella (or if we fight shy of 

 Sturnella, let us say there are only two genera, viz. Trupialis 

 and Leistes). Now in these genera there is a break in the 

 continuity of intergradations in the form of the bill, and 

 because of this break the rule is to consider these two forms 

 as generically distinct ; and here my point, which I fear is 

 rather belated, comes in. If we examine immature speci- 

 mens of these two genera, not only do we find the form and 

 shape of the birds to be identical and with no break, but the 

 colour-pattern is also identical ; and the same may, I think, 

 be said of Sturnella. 



We have, then, in the colour-pattern presented by the 

 immature examples of these forms a phylogenetic or generic 

 link, yet, in the ' Catalogue of Birds,^ Leistes is put into a 

 distinct subfamily away from Trvpialis. My point, there- 

 fore, is this — Can we not and ought we not to make use of 

 such a link, or, rather, ought we not to have sonic way of 

 expressing it so that we may be aware of it ? 



