COURTSHIP ACTIVITIES IN THE RED-THKOATED DIVER. 273 
psycho-neural state ivithin which the particular state of readiness to perform 
the act of coition itself can only occur. 
In so far as they are truly self-exhausting, and not stimulative, they must 
either be considered as biologically functionless, as so many bj^-products of a 
mental organization of the type required to execute the stimulative forms of 
display (c/. the way in which song has in many cases become a biologically 
useless outlet for very various emotional states, as well as subserving its 
primary functions in connection with territory) ; or, as I have previously 
suggested (Huxley, '14), their function must be concerned with keeping the 
pair, in species in which both sexes share the duties of incubation and care 
of young, more closely attached to each other throughout the season. 
Here we must be content to note that both types are " accessory " sexual 
characters, in the sense that their main function, like that of copulatory 
organs, is to facilitate the union of the gametes, and that they represent 
different methods of arriving at the same result — viz., the raising of the 
emotional level of the pair to a point at which coition will take place. 
It may be suggested that to speak of excessive coition, as I have done, is 
to use a phrase which it is difficult to justify biologically. It should be 
remembered, however, that experiment has shown that, in mammals at least, 
a male will, if females in the right condition are provided, continue to pair 
until his seminal fluid contains very few spermatozoa (Hays, '18 ; Lloyd- 
Jones & Hay, '18). Normally, of course, this is prevented in mammals bj'^ 
the fact that the females only attain the condition in which they are ready 
for coition for verj' short periods at a time. A further disadvantage would 
accrue from the absorption of attention in the sexual act which is so marked 
a feature in most animals. The more frequent this might be, the more the 
species would be exposed to the attacks of enemies. The whole subject has 
been fully dealt with by Qroos in his interesting book ' Die Spiele der 
Tiere' ('98) ; and see also Mottram ('14). 
The regulation of coition, however, is undoubtedly not the only factor of 
importance in the evolution of courtship. Previous workers on the subject 
have been too exclusivel}^ preoccupied with the epigamic significance of 
courtship. This was natural ; but they should have remembered that the 
organism is a whole. We find as a matter of fact that the form and extent 
of courtship, nay, in some periods its very existence, is due to causes which 
are not epigamic in origin, but connected with other fundamental biological 
needs in relation with the annual cycle of the animal. 
In many birds, as we shall find (see Howard, '"20), it is of prime import- 
ance for the welfare of the pair and its offspring that a well-defined territory 
shall be occupied in which the nest is afterwards built, and from whose 
produce the young are usually fed. It is a biological advantage to occupy 
territory earlj' ; birds which did not do so until late would find all available 
space taken up, and would have to fight for occupation. When the sexes are 
dimorphic, one will usually be the more active in this task — almost invariably 
