1909 ] Brewster, Barrow's Golden-eye in Massachusetts. 161 



islandica. All the other external characters appear to be quite 

 constant. Perhaps the most important as well as interesting of 

 them all is one which the late Dr. J. A. Jeffries was the first to 

 bring to the notice of ornithologists. It concerns certain of the 

 white and black scapular feathers. With these, as Dr. Jeffries 

 says, 1 "the terminal part of the white breaks off, and leaves the 

 black edges projecting beyond" in Barrow's Golden-eye, whereas 

 "this breakage does not take place in the common Golden-eye." 

 This curious difference has been shown with absolute uniformity 

 in all the specimens that I have ever examined. 



That the males, as well as the females, of americana tend to vary 

 in the direction of islandica, whereas both sexes of the latter are 

 almost wholly free from variability of a corresponding kind, is 

 interesting and perhaps, also, significant — if we could but grasp 

 the underlying meaning of the fact. The approaches shown by 

 the adult males are, however, much less frequent and pronounced 

 than those afforded by the females. Indeed, I have seen only a 

 very few males of americana which were not typical in every essential 

 particular, and I have yet to meet with one which could fairly be 

 regarded as a "half-way" intermediate between that species and 

 islandica. 



Since the adult male of Barrow's Golden-eye differs from that 

 of the common Golden-eye, not only in respect to pronounced and 

 stable external character but in internal structure, also (as Dr. 

 Gilpin has shown), it would seem to be beyond question that the 

 two forms are specifically distinct. Nevertheless they may inter- 

 breed occasionally, as Ducks of other and less closely allied kinds 

 are known to do. If the intermediate birds to which I have alluded 

 were of both sexes and of infrequent occurrence it might be possible 

 to regard them as hybrids or the progeny of hybrids and to explain 

 their various peculiarities by the application of one or another of 

 Mendel's interesting laws — as has been done so convincingly of 

 late in case of certain aberrant Warblers belonging to the genus 

 Helminthophila. But as they appear to be invariably females and 

 by no means uncommon, and as interbreeding of whatever kind is 

 not known to ever produce offspring exclusively of one sex — at 



i Bull. N. O. C, V, No. 3, July, 1880, p. 189. 



