256 MR. JULIAN S. HUXLEY ON 
From the beginniug we noticed that birds engaged in this and in other 
sexual ceremonies, or more often when under the influence of sexual excite- 
ment, but not actually engaged in a ceremony, often engaged in curious and 
apparently meaningless actions. The most frequent was the dipping of the 
beak in the water (fig. 2), often repeated several times within a few minutes ; 
a variation of this consisted in " looking into the water" — in other words, the 
submerging of the beak and fore-part of the head for some little time ; finally, 
shaking of the head was observed, though much more rarely than in the Grebe. 
Fig 2. 
Pied-throated Diver : snake-ceremony. 
It became quite certain, as we continued our observations, that these actions, 
or at least the two former, were definitely associated with sexual excitement. 
Like the head-shaking and " habit-preening " of the Grebe (Huxlej^, '15), 
they appear to represent actions normally performed with some other 
function, or, if functionless, with non-sexual associations, which have become., 
through some peculiarity of the psychological mechanism, secondarily 
associated with sexual excitement, and used as physical expression of sexual 
emotion. This appears also to be the case with a special form of dive which 
I call the "splash-dive." In this, instead of submerging quietly, almost 
Fig. 3. 
Red-throated Diver: emergence ceremony. 
without a ripple, as is done when the birds are diving for food or to escape 
danger, the bird gives a sharp kick with the legs as it goes under, sending a 
shower of spraj^ into the air ; furthermore, the dive is for a very short distance, 
the bird emerging generally about 5 or 6 yards away. This, too, is associated 
with apparently all forms of sexual excitement, and otherwise is used only 
under the influence of the emotion of anger (see Van Oordt and Huxley, 
'22). Here we have apparently a normal form of activity, which is used in a 
modified form when associated with sexual emotion. 
