NATURAL HISTORT — ZOOLOGY. 211 



the equidas was next considered, and the anomalies and difficulties it 

 offers were pointed out ; and lastly the variations which horses offer 

 in their feral and their domesticated condition, were discussed. The 

 questions thus shown to be connected with the species horse, are 

 offered by all species whatever ; and the next point of the discourse 

 was the consideration of the general character of the problem of the 

 origin of species of which they form a part, and the necessary con- 

 ditions of its solution. So far as the logic of the matter goes, it 

 was proved that this problem is of exactly the same character as 

 multitudes of other physical problems, such as the origin of glaciers, 

 or the origin of strata of marble ; and a complete solution of it 

 involves — 1. The experimental determination of the conditions under 

 which bodies having the characters of species are producible ; 2. The 

 proof that such conditions are actually operative in nature. Any 

 doctrine of the origin of species which satisfies these requirements 

 must be regarded as a true theory of species ; while any which does 

 not is, so far, defective, and must be regarded only as a hypothesis 

 whose value is greater or less according to its approximation to 

 this standard. 



It is Mr. Darwin's peculiar merit to have apprehended these logi- 

 cal necessities, and to have endeavoured to comply with them. The 

 pigeons called pouters, tumblers, fantails, &c, which the audience 

 had an opportunity of examining, are in his view the result of so 

 many long-continued experiments on the manufacture of species ; 

 and he considers that causes essentially similar to those which have 

 given rise to these birds are operative in nature now, and have in 

 past times been the agents in producing all the species we know. 

 If neither of these positions can be upset, Mr. Darwin's must be 

 regarded as a true theory of species, as well based as any other phy- 

 sical theory ; they require, therefore, the most careful and searching 

 criticism. After pointing out the remarkable differences in struc- 

 ture and habits between the carrier, pouter, fantail, tumbler, and the 

 wild Coluniba livia, the speaker expressed his entire agreement with 

 Mr. Darwin's conclusion, that all the former domesticated breeds 

 had arisen from the last-named wild stock ; and on the following 

 grounds — 1. That all interbreed freely with one another. 2. That 

 none of the domesticated breeds presents the slightest approxima- 

 tion to any wild species but 0. livia, whose characteristic markings 

 are at times exhibited by all. 3. That the known habits of the 

 Indian variety of the rock pigeon (C. intermedia) render its domesti- 

 cation easily intelligible. 4. That existing varieties connect the ex- 

 tremest modifications of the domestic breeds by insensible links with 

 C livia. 5. That there is historical evidence of the divergence of 

 existing breeds, e.rj., the tumbler, from forms less unlike C. livia. 



Mr. Huxley then analysed the process of selection by which the 

 domesticated breeds had been produced from the wild rock pigeon ; 

 and he showed its possibility to depend upon two laws which hold 

 good for all species, viz., 1. That every species tends to vary ; 2. 

 That variations are capable of hereditary transmission. The second 

 law is well understood ; but the speaker adverted to the miscompre- 



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