280 ME. JULIAN S. HUXLEY ON 
activities of tiie species. For instance, various liawks {e. g. Kestrel and 
Peregrine) have courtships which are based upon the wonderful powers 
of flight possessed by the group ; while many water-birds, like Grebes and 
Divers, show courtships in which some normal aquatic performance is 
sexually utilized. Thus in considering the genesis of courtship ceremonies, 
we have to distinguish between the raw materials and the later speciali- 
zation. The raw materials are (1) coition-attitudes; (2) originally 
non-significant general movements^ especially of feathers, wings, and tail ; 
(3) actions originally connected with activities in themselves associated 
with sexual emotion, such as nest-building ; (4) actions originally sub- 
servient to some non-sexual function. 
Later, specialization consists (1) in the development of striking colour on 
parts prominently displayed in the raw actions; (2) in the development 
of such parts to form special structures {e. g. tail-coverts of Peacock, 
ruff of Crested Grebe). 
The difficult question remains as to the reasons for the existence of 
dimorphism of courtship in some species, but of mutual ceremonies — 
associated, be it remembered, in the majority of species, with special colours 
and structures of as definitely sexual (epigamic) significance as in dimorphic 
forms — in others. 
In general, it appears that it must have some connection with mode of life, 
althouoh in the absence of detailed information on many birds, and of 
statistical treatment, our conclusion cannot be wholly satis factor j-^ at present. 
In the first place, it is undoubted that polygamous species present the most 
extreme cases of male adornment, combined with protective colouring in the 
females. Secondly, in monogamous species with marked male adornment, 
the females are usually protectively coloured, and usually undertake the 
whole of the duties of incubation — e. g. Anatidse, such of the Pheasants as 
are monogamous, &c. In some forms with dimorphic courtship, such as the 
Sylviidfe, the two sexes are often not very distinct, and are both more or less 
protectively coloured ; both sexes may incubate here, although the female 
does so much more than the male. The Sylviidse may be regarded as 
primitive in respect of the evolution of post-mating courtship. The 
Fringillidse are, on the whole, somewhat similar to the Sylviidae, save that 
the colour-dimorphism is usually more marked and the male usually 
incubates less. E. Howard ('20) has recently shown that territory plays a great 
part in the lives of birds, and that, in both Sylviida3 and Fringillidas, it is the 
male who, early in the season, before other manifestations of sexual emotion,- 
occupies a definite territory. Singing then begins, and is associated with the 
possession of territory. The process of mating-up consists mainly in the dis- 
putes of females for occupied territories with their contained males (PI. 15. 
fitr. 7). Since the whole breeding-life of the birds is connectedwith the staking- 
outof territory at the earliest possible oi^portunity by the males, it follows that 
