254 Agassi^ Contributions to the 



cies may have sprung from two or several origins. We cannot 

 be required to assume a cause greater than that which the effect 

 demands ; and if one pair of the American crow or Canada goose 

 would now be sufficient, in a calculable number of years, to sup- 

 ply all America with these species, we need not suppose any 

 more. Even in those cases where one centre of creation appears 

 to be insufficient, this may only be a defect in our information, as 

 to the precise range of the species, its capabilities for accommo- 

 dating itself to external differences of habitat, and the geological 

 changes which may have occurred since its creation. Take the 

 example given at p. 40 of the " Contributions." The American 

 Widgeon and British Widgeon, and the American and British 

 red-headed Ducks are distinct species. The Mallard and Scaup 

 Duck are common to both sides of the Atlantic. The inference 

 is that since the distinct species of widgeons and red ducks were 

 probably created on the opposite sides of the Atlantic, so were 

 the Mallaids, though specifically identical. To prove this is ob- 

 viously altogether impossible; but even to establish some degree 

 of probability in its favor, it would be necessary to show that- the 

 Widgeons and Red Ducks equal the Mallard and Scaup Duck in 

 hardiness, in adaptability to different conditions of climate and 

 food, in migratory instinct and physical powers of migration, and 

 farther, that these species are equally old in geological time. 

 We do not happen to know, in reference to this last particular, 

 which species is the oldest, if there is any difference ; but remains 

 . of ducks have been found in the later deposits, and if it should 

 prove that the species now more widely distributed existed at a 

 time when the distribution of land and water was different from 

 that which now prevails, we should have a case quite parallel to 

 many known to geologists, and utterly subversive of the view be- 

 fore us. The Mallard is also an unfortunate instance, from its 

 well-known .adaptation for domesticity, and consequently proved 

 capability of sustaining very different conditions of existence. The 

 Scaup Duck, hardy and carnivorous, a sea-duck and a good diver 

 and Asiatic as well as European, is probably far better fitted for 

 extensive migration than the Widgeon. It is on such grounds, 

 incapable of positive proof, and with palpable flaws in even the 

 negative evidence, that we are required to multiply the miracle 

 of creation, rather than submit patiently to investigate the psy- 

 chical, physiological and physical agencies involved in one of the 

 most interesting problems of Zoology, the geographical distribu- 

 tion of animals. 



