242 BULLETIN OF THE 



sentatives of species ranging to warm-temperate latitudes are smaller 

 at the northward than at the southward, as is seen in the native dogs, 

 the foxes, and the wolves, and in the arctic races of man. The ex- 

 planation generally given of this seems possibly applicable to the beaks 

 of birds, namely, a greater activity in the circulation of the blood in 

 the peripheral parts of the body in the temperate latitudes. 



Species, Varieties, and Geographical Races. 



The foregoing remarks on individual and geographical or climatic 

 variation necessitates a brief consideration of the character of species, 

 varieties, and races, and the propriety of appl \ ing binomials to such 

 forms as can be clearly shown to be connected by intergrading links 

 with others previously known. As preparatory to what follows, it 

 seems proper to refer briefly to the origin of the excessive synonymy 

 with which our descriptive ornithological works are burdened. 



Ornithological synonymes may be arranged, as regards their origin, 

 under four primary heads, namely: (1) Those arising from the de- 

 scription of immature and adult birds of the same species for different 

 species, (2) from authors mistaking sexual for specific differences, (3) 

 individual variation for specific differentiation, and (4) climatic differ- 

 entiation for specific. A fifth source of error, and one which has given 

 rise to a large class of synonymes, results from a combination of the 

 causes indicated under (3) and (4). 



Synonymes arising from the first two causes mainly preceded the 

 others in regard to the relative frequency of their occurrence, especially 

 so far as regards the birds of this continent. During the previous 

 century, and the first two decades of the present, our birds were mainly 

 described by European naturalists, who had no acquaintance with them 

 in life, and whose resources often consisted of single and imperfect 

 specimens received from chance travellers, without any indication of 

 their sex or age. Later they were studied by resident naturalists, by 

 whom the mistakes of their predecessors in this respect were to a great 

 extent corrected. The laws of sexual and age variation becoming grad- 

 ually known, errors from this source were soon far less frequent than in 

 earlier times. When at a comparatively recent date critical compari- 

 sons were made of specimens from distant localities before regarded as 

 specifically identical, it was found that occasionally distinct species had 

 been confounded. Such results led in the end to undue importance 



