526 MR, J. S. HUXLEY ON THE 
so constructed that impregnation would take place equally well 
whether the sexes are in normal or reversed position : that is to 
say, there is no necessity for keeping to the customary position— 
and accordingly “reciprocal transference” of the pairing atti- 
tudes (whether the transference be apparent or real) may, and 
quite probably will, take place. If so, then in one of our Grebes 
the instincts and reflexes for the pairing-actions proper to its 
sex co-exist side by side with those for the pairing-actions proper 
to the other sex. It is also obvious, first, that both cannot be 
gratified simultaneously ; and, secondly, that these two very 
different sets of actions must be associated with two very different 
sets of emotional states. The bird may ‘“‘feel female” or it may 
“feel male,” and according to its feelings, so will it tend to act. 
But, as we saw before, in discussing the pairing-attitudes, it 
appears that, owing to the difficulty of coition in the Grebe, the 
“female” (passive) pairing-attitude has become a mere symbol 
of readiness to pair. Thus Natural Selection has come in to 
assist the slow process of transference (at any rate, so far as 
pairing-attitudes are concerned), and since whatever involves 
them will probably involve coition itself as well, we have an 
additional reason for believing that actual reversal of pairing 
does take place, as Selous supposes, in the Grebe. 
At any rate, there can be no doubt about the reversal in the 
Pigeon and Moorhen. The sudden reversal that here takes place 
is rather different, but may be explained somewhat as follows :— 
Here, too, both active and passive instincts are now represented 
in either sex. A bird is ina state of sexual excitement ; this 
excitement releases itself in the performance of, say, the male part 
in the act of pairing. The excitement is not always completely 
exhausted by the act, and, if so, the act is repeated (just as the 
shaking-bouts of the Grebes are continued for a longer or shorter 
time, according to the degree of what we may call courtship- 
excitement). But supposing that general sexual excitement 
arouses both the male and female emotional states, then the per- 
formance of the act once in the male attitude will only exhaust 
the feeling of ‘male excitement,” leaving the ‘female feeling ” 
still a-tingle. The result will be, first, an inducement to repeat 
the act and, secondly, an inducement to repeat it with attitudes 
reversed. 
Thus such immediate reversal is more or less an accident of 
heredity, while the Grebe’s reversal is an accident aided by the 
usefulness of the transferred actions, which thus bring the acci- 
dent within the sway of Natural Selection, 
This treatment of the question is of necessity sadly speculative, 
but it is our duty at least to try to construct a coherent mechanism 
of theory to explain the isolated facts of observation. 
Finally, a word as to terminology. J have already pointed out 
(Huxley, ’12,) that the phrase secondary sexual cannot be applied 
to the Grebes’ ruff and ears or to their courtship-actions, because 
