48 THE ZOOLOGIST. 



between these species of Ptarmigan, which are all, be it noted, 

 monogamous. 



Further, the very close relationship which exists between the 

 species, leaving practically nothing but colour and size by which 

 they can be discriminated, makes it quite possible that any one of 

 them should produce occasional varieties in plumage resembling 

 another, from the tendency to revert to the ancestral form. We 

 seem to have a good example of this in the " mottled brown and 

 white variety very much resembling the summer plumage of the 

 Ptarmigan" described by Lord Stanley, and recorded by Montagu 

 as above noted. 



On the whole, however, as Prof. Newton leaves no room to 

 doubt that he himself believes the bird to be a hybrid, I confess 

 that I am on that account, more than on its appearance, disposed 

 to accept it as such, and if only the remainder of the brood had 

 partaken, more or less, of its peculiarities, I think that the 

 circumstantial evidence would then have amounted as nearly as 

 possible to proof positive. 



We have now considered individual cases, and ascertained that, 

 however doubtful most of them may be, it is at least possible, 

 and perhaps probable, that one or more of them are genuine 

 examples of this rare cross. 



It remains to enquire whether, on general grounds, such a hybrid 

 might be expected to occur sometimes ; if this be so, it strengthens 

 by so much the probabilities of the more likely instances, other- 

 wise it diminishes these probabilities to the same extent. 



Now numerous and undoubted instances are on record of the 

 occurrence of hybrids between other members of the Grouse 

 family, as well as a few between them and gallinaceous birds. 

 The following examples may all be accepted as established in the 

 wild state, and I have myself seen specimens of each : — 



(1) Capercaillie (Tetrao urogallus), female, and Blackcock (T. 

 tetrix), male, both species polygamous; hybrids not uncommon. 

 It seems doubtful if the counter-cross ever occurs. (2) Black- 

 cock, male, and Pheasant (Phasianus colchicas), female; both 

 species polygamous. (3) Blackcock and Willow Grouse of Nor- 

 way and Sweden (Lagopus albus), not common; sexes of parents 

 uncertain. (4) Blackcock and Red Grouse (L. scoticus), rare ; 

 sexes of parents uncertain. 



One or two other crosses are alleged, and in addition both the 



