FLICKER 259 



this is a view which cannot at present be disproved ; but it also 

 must be admitted that neither has it been proved. Mr. J. A. Allen 

 was supposed to explain the difficulty {Bull. Mus. Harvard, iii. p. 118) 

 as arising from climatic influences, while Dr. Coues was formerly 

 {B. North-lVest, p. 294) inclined to support that view, but sub- 

 sequently {Key N.-Am. B. p. 492) followed Mr. Ridgway's suggestion 

 {Orn. Fortieth Parallel, p. 556, note) that these birds might be 

 "remnants of a generalized form." If so, a case would be found 

 analogous to that presented by certain forms of Coracias (Roller), 

 and a good many of the Phasianidse, to say nothing of other groups — 

 though strictly intermediate forms are not often met with. So much 

 has been wTitten on what is called the " interbreeding " of species by 

 persons who seem ignorant of the fact that all specialized forms must 

 have sprung from more generalized ancestors, that the careful 

 zoologist will abstain from invoking a theory of " interbreeding " to 

 account for every difficulty that presents itself in the differentiation 

 of species. Granted that most of these generalized forms are by this 

 time become extinct, there is no reason, even allowing for the going 

 on of specialization, why some of them should not still exist, and 

 thus such forms of Colaptes, Coracias, Euplocamus, and Fhasianus sur- 

 vive to this time. Against this view, however, may be set the fact 

 that examples of C. ayresi or hyhridus offer some characters so very 

 pronounced ^ that those who favour the hybrid origin have appar- 

 ently a strongish case.- But then it may be reasonably alleged that 

 zoologists, to their shame, are so absolutely ignorant of the laws 

 that govern hybridity in animals, that no argument can be founded 

 on a presumption that has positively no foundation — for no zoologist 

 has as yet carried out any such series of experiments as has again 

 and again been done by botanists to the very great advancement of 

 their study. Consequently the pheenomena of hybridity in animals 

 can only be interpreted — and possibly wrongly interpreted — by 

 those observed in plants. Among the few experiments hitherto 

 made in regard to Birds, some unmistakably shew how strongly the 

 principle of Reversion works. 



Another interesting fact relating to the genus is that at least 

 one of the South- American members of it, C. agricola, inhabiting 

 the treeless plains of La Plata and Patagonia, has succeeded in 

 accommodating itself to circumstances, — as recorded among others by 

 Darwin {Origin of Species, chap, vi.) under the name of C. campestris, 

 which seems rightfully to belong to a more northern form. Since 

 Azara's time it has been known to frequent the open country, seek- 



^ For instance, an example may be all mexicanus on one side and all auratus 

 on the other ! 



- Since this was in type, Mr. Allen has published [Bull. Am. Mus. N. H. iv. 

 pp. 21-44) the results of an elaborate investigation which he says "tend strongly 

 to confirm Baird's startling hypotheses of hybridization on a grand scale." 



