COURTSHIP OF THE GREAT CRESTED GREBE. 511 
This will, in the first place, show how difficult, and almost 
inevitably futile, it is to try and deal with the emotional essence 
of things by the methods of “ordinary biology”; I think, how- 
ever, that it will serve to explain what I mean by a self-exhaust- 
ing expression of emotion, and will give the point of view from 
which to look at the facts of the Grebe’s courtship: let us now go 
on to examine the facts themselves more systematically. I will 
take the different forms of courtship-action one by one, describe 
their usual occurrence and their relation to other actions, and 
then mention the most important variations or exceptions that I 
have seen. 
The various attitudes already described are combined into 
definite actions or ceremonies. 
(a) The simplest form of courtship-action is the bout of shaking, 
of which I have described a typical example. As already seen, 
shaking may take place either before or after other courtship- 
actions, but in perhaps the majority of cases it is not thus a link 
in a chain of processes, but a single self-originating and self- 
exhausting process. It varies acertain amount in intensity and in 
length, and also in the amount of habit-preening that takes place. 
Of this there may be none, or, towards the end of a bout, there 
may sometimes be more preens than shakes. The bouts seem, to 
the casual onlooker, to start themselves—in reality, I think, each 
bird excites the other. One gently shakes its head under the 
force of rising emotional tension; the other bird had not quite 
got to that stage, but the sight of its mate shaking acts as a 
stimulus, and it too pricks up its head a little and gives a shake. 
This reacts on the first bird, and so the excitement is mutually 
increased and the process fulfils itself—a very good example of 
“‘ crowd-psychology,” and also a good example of an epigenetic 
process *, 
There is one well-marked variation of this form of courtship 
which seems to denote a higher level of excitement ; it is especi- 
ally common when a third bird has intruded into the domestic 
harmony of the pair and has been driven off (section 5, iv.). 
Here the beaks are pointed somewhat downwards, the neck 
brought a little forward instead of vertical, the whole head 
brought forward and curved over, and the ruff erected more than 
usual (fig. 6). This attitude is almost always confined to the 
beginning of a bout, the birds sooner or later relapsing into the 
ordinary position. 
The bout of shaking is not only the commonest form of court- 
ship-action, but it also forms part of all the other more elaborate 
forms. It always ends the series of actions, and often begins 
them as well. It is as it were the foundation on which they are 
built, and was probably (if I may express a mere opinion) the 
earliest to appear in phylogeny. 
The other ceremonies of courtship are all formed by the 
* See also p. 544, where one bird won’t shake, and the other wants to. 
