508 MR. J. S. HUXLEY ON THE 
from pairing with her, by simply running or flying away 
(cf. the Redshank, Huxley, ’12,). In our Grebe we are a step 
further still: not only must the female (or the passive bird, if we 
want to be precise; but this is, for the present, complicating the 
issue unnecessarily) be willing to pair, but she must also take the 
first steps-—-must ascend a nest or platform and assume a special 
position—before the cock can think of pairing. Here, therefore, 
supposing that the functions of the sexes had not been almost 
equally distributed, it would have been necessary for the hen to 
have had a strong impulse towards pairing ; it might be that she 
was impelled directly by a violent physiological stimulus, or 
more indirectly by association, through the act being extremely 
pleasurable. 
The phylogenetic course of events is hard to disentangle; we 
might suppose it to have been somewhat as follows :— 
(1) Owing to the need of a firm support for pairing, it became 
necessary, as above set forth, for the female to take the initiative 
in the act of pairing, by assuming a special position. 
(2) The male had thus no means of expressing his readiness 
to pair [whereas in most monogamous birds it is the male, as 
one would expect, who takes the initiative: cf the Warblers 
(Howard, ’13), the Redshank (Huxley, ’12,), ete.]. 
(3) Meanwhile, quite independently, a process, or tendency — 
eall it what you will—had shown itself, by which the characters 
of one sex might be or tended to be transferred to the other, and 
vice versa. 
(4) This was seized upon by Selection (we cannot as yet speak 
less metaphorically) and employed to supply the present want ; 
the pairing attitude of the female was transferred to the male to 
give him, too, a means of expressing his readiness to pair—to 
enable him, should he wish it, as well as the hen, to take the first 
step towards the performance of the act of copulation by the pair. 
(5) As so often oceurs, the process did not stop precisely at 
the desired spot (we still speak in metaphors, for brevity’s sake) ; 
with the female pairing-attitude was transferred the female 
pairing-instinct, and so came about the complete or nearly 
complete facultative reversal of the pairing habits. ; 
This naturally does not pretend to be more than a possible 
scheme ; but it is worth while setting out such a scheme, merely 
. aa how this ‘reversal of the sexes” could have come 
about. 
(ii.) Courtship. 
T have started with the subject of coition, because the first 
thing I want to make clear about the courtship-actions is their 
total lack of connection with the act of pairing itself—a notable 
fact, in which the Grebe differs radically, of course, from many 
other birds, especially those in which the sexes differ in appear- 
ance, é.g. the Bustard or the Peacock, but also some in which the 
sexes look alike, e.g. the Redshank. 
