5O4 MR. J. 8S. HUXLEY ON THE 
to pair is made, and the active bird jumps up apparently 
at once, without any delay. In the case observed by me the 
active bird seemed very definitely to examine the passive one, 
poking its beak down close to it; but the examination was very 
short, the attempt at pairing following immediately. 
When the active bird is moderately eager but not quite eager 
enough to attempt to pair, it may swim up to the passive bird 
a number of times, each time make as if to spring up, and then 
decide not to, but swim away again. 
The assumption of the passive attitude by one bird is generally, 
so far as I can see, used as an invitation to the other bird to 
pair: perhaps I should express myself rather differently, and say 
that it always denotes readiness to pair, and is generally used as 
a primary excitant—i. ¢., it is the first sign given by either of the 
birds of readiness to pair. This is well brought out by incidents 
such as this:—Both birds are building the nest; suddenly the 
hen jumps up on to the nest and goes into the passive attitude, 
every now and then raising her neck and looking round at the 
cock (Selous, op. cit.). At other times it may be only a secondary 
excitant—a mere symbol, This may happen when one bird is 
sitting and the other approaches the nest; the sitting bird may 
then assume the passive position at each approach of the other. 
Here the approach is the primary stimulus, and the assumption 
of the passive attitude is called forth by it, and not by internal 
causes. In this second case a less degree of ‘‘ sexual feeling” is 
presumably needed to induce the passive attitude than in the 
first case. 
But we are going too fast. We must not omit to notice the 
curious action of the cock in himself copying the hen’s passive 
attitude. This action—one bird going into the passive attitude, 
the other coming up and examining it, and then going off and 
assuming the same attitude—appears only to occur when the first 
bird goes into position on the open water (and not on the nest), 
and even then not always. It seems, however, to happen in the 
majority of cases (though we are perforce generalizing from very 
few instances). It looks as if it were a signal to the first bird 
that the second was ready and willing to proceed further in the 
matter; for the birds after this may proceed together to the nest, 
where the first (Joc. cit. p. 180) or the second (ibid. p. 456) bird 
ascends the nest and assumes the passive attitude once more. 
In other cases, however (ibid. pp. 179, 454), the affair ended with 
the second bird’s assumption of the attitude. Here it looks as if 
a ritual ceremony was developing out of a useful action (see 
below). 
As regards the actual act of pairing (or its attempt, which for 
our present purpose comes to the same thing), the two sexes seem 
here also to play interchangeable roles. In 1900 Selous saw three 
attempts to pair, one apparently successful, two unsuccessful : 
in all three cases the active bird was the larger of the pair.. 
In 1901 he saw two attempts, both of which he thinks were 
