8626 Notices of New Books. 



that I need make no apology for extracting them. The hypothesis 

 that a race may so alter, under altered conditions, that its differences 

 shall become specific or generic, is asserted and maintained by Mr. 

 Darwin and his followers ; and the imposing array of facts, exhibiting 

 such differences in progress, does as great credit to the industry, as 

 the candid method of reasoning does to the ingenuous character of 

 the author. Tn such cases as that of the roller, to which Mr. Jerdon 

 alludes, I admit it is very easy to take either side of the question: the 

 different geographical types may be called, or may be proved to the 

 perfect satisfaction of one or other disputant, races, varieties or spe- 

 cies ; but supposing that geographical conditions can thus establish 

 communities of individuals which a competent ornithologist shall de- 

 scribe and name as species, what shall we infer from this ? Or, 

 admitting that man, carrying out this capability for variation, can 

 breed greyhounds, pug-dogs, Newfoundlands and King Charleses, or 

 among birds all the varieties of pigeons and poultry, what shall we 

 infer from this ? Will it be asserted that any type of roller, dog or 

 pigeon, exhibits and maintains an intermediate position between rol- 

 lers, dogs and pigeons as they are and the acknowledged species, to 

 which they are respectively more nearly affined ? Does not the 

 very existence of geographical races prove the homogeneity of some 

 group of higher value than that race ? It has been said that all ihe 

 allied rollers will interbreed just in the same manner as dogs or 

 pigeons, and that their progeny will be equally fertile : the only con- 

 clusion I can draw from this is that we must extend the imaginary 

 limits we have hitherto made for a species. It will be seen that Mr. 

 Jerdon does not consider the fact of interbreeding freely to be any bar 

 to the distinctness of species : where, then, are we to look for a 

 boundary-line ? 



Nothing appears to me more certain than that the change of spe- 

 cies into geographical sub-species, and the advance of these to real 

 species, necessitates the constant and enormous numerical increase of 

 species. Is this the case ? Is this increase of species proved ? 

 There is another point of view. It does not follow that because 

 a roller is called Coracias indica when inhabiting one district, and 

 Coracias affinis when inhabiting another district, — it does not, I 

 say, follow that either race is advancing towards or receding from 

 a given type : there is no evidence supposed, much less ad- 

 duced, that indica has not always been indica, and affinis always 

 affinis. There is no evidence even of change, leaving advance or de- 

 cadence out of the question ; but there is evidence, positive evidence, 



