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-West, p. 294) inclined to support that view, but sub- 
sequently (Key N.-Am. B. p. 492) followed Mr. Ridgway’s suggestion 
(Orn. Forticth 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 Phasianidx, to say nothing of other groups— 
though strictly intermediate forms are not often met with. So much 
has been written 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, Kuplocamus, and Phasianus sur- 
vive to this time. Against this view, however, may be set the fact 
that examples of C. ayresi or hybridus 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 phenomena 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 cireumstances,—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- 
1 For instance, an example may be all mexicanws on one side and all auratus 
on the other ! 
2 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.” 
