The Development Theory: A Review. 117 



laws of nature to take their course cannot the production of such 

 forms be avoided or prevented ? 



Among domesticated animals human selection is by far the 

 most potent factor. " It was said that in England the intro- 

 duction of short-horned cattle operated almost like a pestilence 

 in the destruction of the earlier and less-improved breeds. The 

 comparison means that the owner of the old sorts killed them off 

 for meat at such a rate as to thin them out as fast as the cattle- 

 plague could have done." Yet the short horns would be ill- 

 fitted to hold their own in a free-fight for existence among long- 

 horned competitors. Man, however, finds that they come more 

 quickly to maturity, are consequently cheaper to raise, and their 

 meat is of fine quality. Hence he decides that they shall live, 

 and the long-horned races go down before them. 



One of the most interesting chapters in the book is that which 

 treats of mimicry, a doctrine which maintains that among the 

 processes of natural selection is one whereby varieties accident- 

 ally possessing characters belonging to other species, and deriving 

 benefit therefrom, transmit that character to their offspring, and 

 a species arises that resembles or mimics the other. This is one 

 of the most curious fields in the domain of evolution, and one 

 which will reward, as well as any, patient and careful observa- 

 tion. Yery little is at present known on the subject, but that 

 little is strongly suggestive to the thoughtful mind of the 

 intensity of the struggle for existence, and the minuteness of the 

 difference on which success or failure may depend. We must refer 

 the reader to the work for examples of this doctrine and for 

 others illustrating the keen competition among plants and 

 insects for mutual advantages in the fertilization of the former 

 and the feeding of the latter. 



The marvellous testimony of embryology to evolution is next 

 considered ; and some of the leading well-ascertained facts detailed. 

 These point like index-fingers to a common ancestry for all 

 living beings, they point along converging roads to it spot at some 

 epoch in the past, where all these diverging ways started from a 

 common centre. No one in this country has contributed so much 

 to the embryological argument in favor of evolution as Prof. L. 

 Agassiz, himself one of its most determined opponents. The 

 close and accurate study of the antenatal history of organic 



