9H THK ZOOLOGIST. 



in case of the rarer forms, the generalisations reached have been 

 based on hundreds of examples of each species and subspecies, 

 gathered from every portion of the habitat of the form in 

 question. The elaboration of this material has resulted in the 

 discovery of intergradation between forms whose specific dis- 

 tinctness was not previously even questioned, and which would 

 now pass as well entitled to specific recognition were the 

 connecting links unknown. Furthermore, it has been found 

 that various portions of the continent present phases of diffe- 

 rentiation, more or less strongly marked, peculiar to each, and 

 which affect the greater portion of the species by which they are 

 inhabited ; while the intermediate and connecting regions furnish 

 a gradual transition between the forms typical of the remoter 

 districts — a transition as gradual as, and correlated with, the 

 changes in the geographical and climatic conditions of the 

 connecting area. In other words, these investigations have led 

 to the recognition of certain general laws of geographical variation 

 which are accepted by all of our ornithologists of recognised 

 authority. 



In consequence of the accumulation and study of this immense 

 amount of material it has been found that three, four, or even 

 half a dozen species formerly in good standing, because known 

 from only a few examples, really form one specific group, with 

 more or less strongly differentiated types in different portions of 

 the general habitat, which, however, are inseparably connected by 

 series of examples from intermediate districts. While all these 

 intergrading forms are, in consequence of their known inter- 

 gradation, referred to a single species, each differs so much from 

 the other, as they approach their extreme phases of divergence, 

 that the differences seem too great to pass unnoticed, and are 

 therefore recognised nominally, and at the same time in such a 

 manner as to indicate their true status and relationship. The 

 forms trinominally designated are simply well-marked local forms, 

 geographical races, incipient species, subspecies, or " varieties," 

 in the sense in which the latter term is commonly employed. 



To refer now to the text which has given rise to this bit of 

 preaching, the writer says : " For instance, to take the first 

 example in the ' Check List,' if Turdus migratorius propinquus is 

 not Turdus migratorius, why not let it stand as Turdus pro- 

 pinquus?" To this we answer, because it would be giving 



