COURTSHIP OF THE GREAT CRESTED GREBE, 523 
The courtship actions, however, can scarcely be explained by 
transference. ‘The Penguin-dance, for instance, can never have 
been anything but a joint ceremony, equally shared by both sexes. 
Furthermore, even in the Dabchick, although it (and it alone in 
the subfamily) lacks all courtship-structures on the head, there is 
a joint courtship-action—the two birds come face to face, stretch 
up their necks, and emit the well-known cry. This being so, it 
is fairly clear that the ancestral courtship-actions of the Grebes 
were not in the nature of a display by one sex, but were joint 
actions of the pair. ‘There is nothing especially remarkable in 
this. The display-courtships are, on the whole, more striking, 
and so have been more frequently described ; but (to draw on my 
own limited experience) Razorbills.and Herring-Gulls have very 
well-marked joint courtship-actions, although the actions are 
associated with no special structures whatever, and Selous has 
described other such actions in Swans, Divers, Guillemots, 
Fulmars, and other species. 
I should put forward the theory that the courtship-habits of 
birds are based upon at least two totally different foundations : 
in the first place the actions gone through by males alone, appa- 
rently as the direct result of sexual eagerness (solitary actions), 
and, in the second place. the actions gone through by male and 
female together, and perhaps often (though by no means always) 
connected or associated with nest-building (combined actions). 
Primitively in neither case would there be any special structure 
or colour associated with the action. For solitary actions this is 
well seen in the dowdy Warblers, so fully described by Eliot 
Howard; here the cocks resemble the hens, but go through 
elaborate droopings of wings and fannings of tail, with bristlings 
-of feathers on throat and crown. Later, Sexual Selection has 
stepped in, and naturally enough has taken what was already 
given, and added to it. The same instinctively-displayed parts— 
wings and tail, throat and crown—are the parts which are 
especially singled out for the development, first of special colours 
(Finches, Woodpeckers), then of special colours and structures 
combined (Turkey, Argus Pheasant, Blackcock, etc.). In com- 
bined actions a similar process has been gone through. In the 
Herring-Gull and Razorbill we have the instinctive actions pure 
and simple—a direct outcome of nervous excitement. Then, 
again, something has stepped in and used what was thus provided, 
and we get combined actions displaying colour (coloured mouths 
of Fulmar Petrels, Selous), and finally colour and structure, as in 
the Grebe. The members of the Heron tribe in general, and the 
Egrets in particular, have also ornamental structures common 
to both sexes; it would be very interesting to know the course 
of courtship in these birds. Pycraft (13) figures a mutual dis- 
play executed by the Kagu. 
The question now arises, How have such colours and structures 
arisen? By Sexual Selection followed by transference, or by 
Proc. Zoou. Soc.—1914, No. XXX VII. 37 
