Miscellaneous. 345 



The speaker pointed out that these resemblances did not justify us 

 in considering the Palceotherium as a more generalized type, any 

 more than the resemblance of a father to his four sons justifies us in 

 considering him as of a more generalized type than theirs. 



The geographical distribution of the Equidce 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 w^th the species Horse 

 are offered by all species whatever ; and the next point of the dis- 

 course was the consideration of the general character of the problem 

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

 conditions 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 require- 

 ments must be regarded as a triie theory of species ; while any which 

 does not, is, so far, defective, and must be regarded only as a hypo- 

 thesis whose value is greater or less, according to its approximation 

 to this standard. 



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

 logical necessities, and to have endeavoured to comply with them. 

 The pigeons called Pouters, Tumblers, Fantails, &c., which the au- 

 dience 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 nei- 

 ther of these positions can be upset, Mr. Darwin's must be regarded as 

 a true theory of species, as well based as any other physical theory ; 

 they require, therefore, the most careful and searching criticism. 



After pointing out the remarkable differences in structure and 

 habit between the Carrier, Pouter, Fantail, Tumbler, and the wild 

 Columba 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 approximation 

 to any wild species but C. lii-ia, whose characteristic markings arc 

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

 variety of the Rock Pigeon (C intermedia) render its domestication 

 easily intelligible. 4. That existing varieties connect the extremest 

 modifications of the domestic breeds by insensible links with C. livia. 

 o. That there is historical evidence of the divergence of existing 

 breeds, e.g. the Tumbler, from forms less unlike C. livia. 

 Ann. 6,- Mar/. N. Hist. Ser. 3. Vnl. v. 23 



