162 Brewster, Barrow's Golden-eye in Massachusetts. [ April 



least among birds — it appears improbable, to say the least, that 

 hybridity can have had much if anything to do with the present case. 

 The theory of mutation, so much discussed of late, is perhaps worth 

 considering in this connection for it may throw light on some of our 

 present difficulties. It has been tested, I believe, chiefly if not 

 solely by observations made on domesticated animals and culti- 

 vated plants. Some of these are said to have furnished proofs that 

 elementary, yet strongly characterized and apparently stable, spe- 

 cies may originate from other and more variable ones by w r hat are 

 termed "jumps" or "steps." A striking example of this is given 

 by Danvin who, it is now claimed, recognized some of the princi- 

 ples of mutation although he did not deal with them under that 

 name. He says that "japanned" or "black-shouldered" Peacocks 

 have appeared "suddenly in flocks of the common kind" and that 

 they "propagate their kind quite truly," constituting what is con- 

 sidered by good authority to be a "distinct and natural species." 

 Even more remarkable is his statement that they tend "at all times 

 and in many places to reappear," by which he means, apparently, 

 that a long "jump" which gives immediate birth to a well marked 

 form breeding true to type may be followed at rather frequent 

 intervals by precisely similar "jumps," with identically the same 

 results. More recent observations, relating mainly to carefully 

 controlled or fostered plants and animals, have seemed to confirm 

 this surprising fact and to show further that there are species which 

 throw off, thus abruptly, not only strongly characterized and con- 

 stant forms, but also great numbers of less pronounced and stable 

 ones. In other words mutations w 7 hich yield no very important or 

 lasting results appear to occur oftener than those w 7 hich result in 

 the establishment of what are known as good species. 



Since these wonderful things are thought to take place among 

 animals and plants under domestication why may they not happen 

 — if less often — in untrammeled Nature ? It has been inferred 

 that they do so happen but the fact remains to be proved, I believe. 

 If w r e might assume, as a mere tentative proposition, that Clangula 

 islandica is a simple mutant of amcricana, resulting from a long 

 "step" (or succession of "steps") taken in the more or less remote 



1 Animals and Plants Under Domestication, New York, 2d ed., 1876, Vol. I, pp. 

 306, 307. 



