560 MR, J. 8S. HUXLEY ON THE 
special variation in the form of action, in itself proves that 
such preferential mating may and does occur. 
The first modification of Darwin’s ideas leads to a second—to a 
modification of the way in which Sexual Selection works. If 
display is normally an excitant, then there is no ‘“ need” for a 
preponderance of males, nor for actual rivalry between several 
males. Selection is primarily a matter of level. The female does 
not choose the “ best” out of a bunch of suitors ; but those males 
in which the ornaments and display-habits do not reach a certain 
standard, will not be able to raise the female’s emotional state to 
the requisite pitch, and so will die without offspring. (‘This state- 
ment as it stands goes too far; it will serve, however, for the 
time, to show the general idea.) 
This primitive condition has been modified in two ways (and 
on the existence of these two quite distinct lines of development 
I feel Mr. Pycraft has not laid sufficient stress). In the first 
place, in polygamous and polyandrous (and perhaps “ promis- 
cuous ”?) species there may bea rivalry between several males 
in the presence of the females, as in the Ruffand Prairie Hen. 
Jn the second place, the line of mutual selection was started. 
Whether in origin mutual displays too acted as excitants, it is 
not yet possible to say until more observations are at hand. That 
such may be the case, is possible from some observations of my 
own on the Herring-Gull. At any rate, in specialized forms of 
this form of courtship, such as that of our Grebe, this excitatory 
function is completely in abeyance. 
With Mr. Pycraft’s insistence, first, on the principle of Ortho- 
genesis and its importance for the origin of sexual (and other) 
forms of ornamentation, and secondly, on the necessity for a 
psychological pomt of view in our interpretation of the courtship- 
phenomena of animals, I am in entire agreement. 
List or LrreraturReE. 
713. Howarp, H. Exior.—The British Warblers. Parts 1-8. 
Londen, 1907-13. 
*12,, Huxuey, J. S.—A First Account of the Courtship of the 
Redshank (Yotanus calidris Linn.). 
P. ZS. 1912, pp. 647-655. 
Z12.. " 55 The Great Crested Grebe and the idea 
of Secondary Sexual Characters. 
Science, n. s. vol. xxxvi. pp. 601— 
602. 
"11. Pycrarr, W. P.—Habits of the Great Crested Grebe. 
Bield, vol. exviii.- Oct.. 7, @l9ii 
pp. 823-824. 
ES, ° The Courtship of Animals. Hutchin- 
son & Co. London, 1913. 
