COURTSHIP OF THE GREAT CRESTED GREBE, 509 
In relation to this, no doubt, is the fact that pairing only takes 
place on the nest, and that the nest is hidden away among the 
reeds, while the courtship actions are, I believe, aly ays gone 
through out on the open water. This, i in itself, ‘would not be 
conclusive evidence of total separation of the two sets of actions, 
for the performance out in the open might be followed directly 
by a veturn to the reeds and subsequent pairing. But there are 
two further facts which make it conclusive. In the first place, 
one of the reservoirs at Tring is completely bare of reeds, and con- 
sequently of Grebes’ nests too. Itis, however, the richest in fish, 
and numbers of Grebes fly over to it from the other reservoirs 
every day, and at all hours of the day, to feed. Now, in spite of 
the absence of reeds, and so of nests, and so of the possibility of 
pairing, the birds interrupt their fishing, or sleeping, or preening, 
to go through the ritual of courtship just as often on this 
reservoir as on any of the others. ‘That is point number one. 
Point number two goes still further. 
I frequently kept individual pairs under observation for a 
considerable length of time, and then, if I watched long enough, 
always found that one set of courtship-activities would in point 
of fact be followed by a pretty long interval of resting or fishing, 
and that then this time spent in every-day affairs would be 
again succeeded by another series of courtship-actions—a proof 
that these actions are what we may call self-exrhausting and not 
excitatory. The best record, because the longest, was on this 
same reedless reservoir. J had one pair under observation for an 
hour and forty minutes (section 10, record 11). During that time 
they had six simple bouts of shaking, and also two prodigious 
long bouts, followed each time by the diving for weed and then 
the strange Penguin-dance. And between all these elaborate 
displays of sexual emotion, no sign (or possibility) of pairing— 
nothing but swimming, resting, preening, and feeding. 
I was thus—much against my preconceived ideas—driven to 
think of all the complicated postures and evolutions of courtship 
in the Grebes as being merely an expression of emotion. 
The particular form of expression used is no doubt determined 
—predetermined—by the arrangement and innervation of certain 
structures which the birds possess: but the impulse to use the 
muscles and nerves is an emotional one—during courtship there 
must be in the mind of the bird an excitement, a definite feeling 
of emotion. Let us, to satisfy the physiologists, try to put it m 
terms of nerve-currents. One member of a pair is continually 
seeing its mate at its side. This, in its present physiological con- 
dition, stimulates certain tracts of its brain, charging them up and 
up until they are in a state of considerable tension (mental accom- 
paniment:—state of diffused emotional excitement). Finally, 
the tension reaches the critical point, and a discharge follows. 
This discharge flows down hereditarily-determined paths, and 
actuates the muscles concerned in courtship (mental accom- 
paniment :—violent and special emotion, quickly dissipating 
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