270 MK. JULIAN iS. HUXLEY ON 
in passing that there is evidence o£ this direct competition (using the word 
in a metaphorical sense) between males in at 'any rate some polygamous 
species, e. g. the Blackcock (Selous, '09)'. What, then, is the function of the 
sexual adornments and ceremonies — for the most casual observation is enough 
to convince anybody that they possess some function ? 
It is to be observed that sexual ceremonies and colours or structures which 
are displayed solely or chiefly during such ceremonies are only to be found 
in animals of a certain grade of nervous organization. Observation on 
newts, which are remarkable in that the males deposit their sperm in the 
form of spermatophores first and afterwards go through their display 
ceremonies, indicates that the function of the display is a stimulative one, 
designed to stimulate the female to pick up the spermatophore (quoted in 
Pycraft, '13). The experimental work of Sturtevant ('15) on iJrosophila 
entirely corroborates this view. The male in this species performs special 
actions with his wings when " courting " the female. Sturtevant found that 
males with the wings cut off, when imprisoned singly with females, succeeded 
in copulating, but after a longer time than normal males in a similar 
situation. On the other band, when each female was placed with two males, 
one normal, the other with amputated wings, it was found that the wingless 
males were successful in copulating almost as often as were the normals. 
This can only be interpreted to mean that the wing-waving ceremony 
stimulates the female in such a way that she is then ready to receive 
any male in copulation. Morgan ('19). appears to adopt this attitude in 
viewing the whole sexual selection problem, but his statements are not 
very definite, and he does not bring first-hand observation to bear on the 
question. 
Observation of most of the post-mating courtship ceremonies of birds 
bears out this interpretation. If we for a moment confine ourselves to 
a consideration of birds with distinct sexual dimorphism, either of 
colour and structure,- or at least of behaviour, we can say (1) that the 
female is always or usually at a lower level of sexual emotion than the 
male ; (2) that the nervous organization of birds is so advanced that 
behaviour is no longer merel}"- reflex, but that it depends in the main on 
highly-developed instincts, each associated with a particular emotional 
tone. The centres for the instinct require to be stimulated before the 
impulse to the particular instinctive action is felt ; thei'e is a certain 
minimum intensity of stimulation necessary, which, as we have just said, 
is, in the case of the sexual instinct, generallj'- higher in the female than 
in the male ; (3) that, accordingly, a necessary preliminary to coition is 
the raising of the emotional state of the female to the level at which her 
sexual instinct is stimulated to action. 
If we like to sum it up from a slightly different angle, we can say that in 
birds (as well as in other groups), mental organization has reached a pitch at 
which the higher centres concerned with emotion play a predominant part in 
