230 Animal Life and Intelligence. 



wild birds. There can be little doubt that, as he suggests, 

 the Scotch red grouse is derived from a form \vhich, like 

 the -wide-ranging willow grouse, has white winter plumage. 

 During the glacial epoch this would be an advantage. 

 " But when the cold passed away, and our islands became 

 permanently separated from the mainland, with a mild 

 and equable climate, and very little snow in winter, the 

 change to white at that season became hurtful, rendering 

 the birds more conspicuous, instead of serving as a means 

 of concealment." The red grouse has lost its white winter 

 dress; but occasional reversions point to the ancestral 

 habit. 



That crossing tends to produce reversion is a fact 

 familiar to breeders and fanciers, and one which is 

 emphasized by Darwin. When pigeons are crossed, there 

 is a strong tendency to revert to the slatey-blue tint and 

 black bars of the ancestral rock-pigeon. There is always 

 a tendency in sheep to revert to a black colour, and this 

 tendency is emphasized when different breeds are crossed. 

 The crossing of the several equine species (horse, ass, etc.) 

 "tends in a marked manner to cause stripes to appear on 

 various parts of the body, especially on the legs," and this 

 may be a reversion to the condition of a striped and zebra- 

 like ancestor. Professor Jaeger described a good case with 

 pigs. " He crossed the Japanese, or masked breed, with 

 the common German breed, and the offspring were inter- 

 mediate in character. He then recrossed one of these 

 mongrels with a pure Japanese, and in the litter thus 

 produced one of the young resembled in all its characters 

 a wild pig ; it had a long snout and upright ears, and was 

 striped on the back. It should be borne in mind that the 

 young of the Japanese breed are not striped, and that they 

 have a short muzzle and ears remarkably dependent." ' 

 Darwin crossed a black Spanish cock with a white silk hen. 

 One of the offspring almost exactly resembled the Galln* 

 bankiva, the remote ancestor of the parents. 



Such cases would seem to show that in our domestic 

 * Darwin, Animals and Plants under Domestication," yoL ii. pp. 17, 18. 



