^°'g^^^^] Recent /J/mifure. 69 



entirolv to the impulse to breed. (5) Tlie true home of tlie species is its 

 winter area, tiiis being also its original centre of dispersal. (6) Autumn 

 migration is thus a return to winter haunts or centres of dispersal, undci' 

 what he terms a nostalgic impulse, or homesickness; scarcity of food, 

 either present or prospective, decrease of temperature, or any other adverse 

 conditions, have nothing whatever to do with the inception of this 

 autumnal movement. 



This is a brief outline of Mr. I^ixon's premises and conclusions. \n 

 analysis of his evidence shows that they rest mainly on personal ' belief,' 

 and novel assumptions unsupported by any considerable array of facts. 

 He makes repeated reference to -his study of " pre-glacial distribution," 

 and to his " investigation of post-glacial emigration," as having con- 

 vinced him respectively that a southern emigration, or a southern 

 migration, "to escape adverse climatic conditions is a myth," and that 

 "range extension trends in only two directions," namely, fiom the 

 equator towards the poles. Unfortunately the evidence that has led to 

 these convictions is not disclosed, at least in any formal way. 



In discussing his ' law of dispersal,' he says it elucidates "almost innu- 

 merable facts of dispersal which have hitherto baffled all attempts to 

 explain them." Among these is the absence of tropical forms in tem- 

 perate latitudes, etc. It is "obvious, however, that the influence of 

 temperature in limiting the dispersal of species is a factor in the problem 

 that has either never occurred to him, or else is one which he chooses 

 to studiously ignore throughout his work. 



It is, on the whole, perhaps hardly worth while to take Mr. Dixon 

 seriously, inasmuch as he shows no great knowledge, in the first place, 

 of the elements of the problem he proceeds to treat so confidently, which 

 is no less than the origin of life in genei-al and an explanation of its 

 present geographical distribution ; yet, so far as his book shows, he has 

 never thought of it in that light. To him it is simplj- the migration of 

 birds, which involves incidentally questions of their geographical origin 

 and distribution, although he mav be supposed to refer to life in general, 

 especiall}' in speaking of his grand discovery of what he terms the "Law 

 of Life's Dispersal." Birds of course are not to be treated as a group apart 

 from the rest of the animal kingdom, but as subject to the same general 

 laws of dispersal as other animals, and even plants. On this an appeal to 

 the geological record is fatal to our author's grand conceptions, who, 

 though referring often to his " preglacial investigations," gives no evidence 

 of knowing anything of either geological or biological conditions prior 

 to the Ice Period. He is thus free to construct, remove, or transpose con- 

 tinents and seas to suit his hypotheses of bird migration, as well as to 

 assume breeding areas that do not exist, simply because there should be 

 such breeding areas to render his theories of both migration and dispersal 

 in any degree tenable. 



It is therefore to be reoretted that a work so full of information for the 



