The Zoologist— December, 1873. 3791 



As regards Mr. Allen's work, I am not only willing, but desirous, 

 that he should receive all the credit due to him for his well-accom- 

 plished task of elucidating the laws of climatic colour-variation, and 

 geographical distribution. This gentleman's writings place him 

 in the foremost rank of the philosophical ornithologists of the 

 present day, their high merit and great importance being recog- 

 nized by all to whom they are familiar. I have the highest 

 respect for Mr. Allen's works ; they show careful study, deep 

 thought, persevering search for facts, and thorough, analytical 

 mode of treatment. About their only fault consists in the too 

 frequent evidence of conclusions "jumped at," or based upon 

 insufficient evidence. 



But as justly as Mr. Allen deserves his high position among the 

 most thorough and advanced ornithologists of the day, we must 

 not lose sight of the fact that he is not the only one who has 

 written upon the subject of climatic colour-variation and geogra- 

 phical distribution. Professor Baird, the pioneer in this subject, so 

 far as America is concerned, first made known the main governing 

 laws, and thus opened the way to later researches. But even he is 

 preceded by Dr. Gloger, who anticipates all American writers in 

 many generalizations of this kind, published as long ago as 1833.* 



A few of Dr. Gloger's generalizations, which bear more directly 

 upon the province of this paper, are the following: — 



" The variation in colour of birds from one country to those from 

 another, is influenced not only by the mean temperature of the 

 year, but also by that of single months (those about the time of the 

 most rapid growth or moult) and by the relative time and quantity 

 of the falling snow and rain:' '* Light also has influence " — in the 

 change of colour. " Heat has influence by drying out the moisture, 

 whereby the action producing a change is a mechanical one." 

 "The fact that in some summers there are more cuckoos of a 

 reddish brown colour, or with reddish brown spots, may probably 

 be owing to the general or periodical atmospheric constitution of 

 the year in question." 



In 1866, before the appearance of any of Mr. Allen's writings, 

 Professor Baird published a paper entitled " The Distribution and 

 Migrations of North American Birds," t in which much was said 



* "Das Abandern der Vogel dursch Einilufs des Klimas." By Dr. Constantia 

 Lambert Gloger, Breslaw, 1833. 

 t ' American Journal of Science and Arts,' Vol. xli., Jan. and March, 1800. 



