224 THE ZOOLOGIST. 



out of the primary sexual emotions, and if the nest is the out- 

 come solely of constant small acts of intelligence of a constructive 

 kind, a bird, when building, should be in a very different state 

 of mind from that in which it is when under the influence of 

 passion. The two things, instead of being mentally associated 

 together, through their common origin and consequent habitual 

 concomitancy, might be expected to be cut off from each other ; 

 nor would Natural Selection, as far as one can see, have at all 

 tended to favour their union. Nor does she, upon the view 

 which I advocate. On the contrary, she must be looked upon 

 as a differentiating and specialising agency, whilst she at the 

 same time makes use of the force of heredity. She has changed 

 one trifling and wholly irrelevant instinct that arose, rhyth- 

 mically, as a mere nervous adjunct of the sexual stimulus, into 

 the important one of nidification ; and if she has not yet 

 eradicated all traces of the steps by which she has brought this 

 about, yet she is, as it were, constantly striving to do so, since 

 the tendency must be for mere useless actions, representing a 

 waste of energy, to drop out aud disappear before useful ones. 

 Again, there seem many reasons against a habit of pairing on the 

 nest, arising, as it were, peraccidens. If it is continued after the 

 laying of the eggs (as I have reason to think that, in some cases, 

 it still is), these may, in consequence, suffer; nor does an artificial 

 structure seem to offer any particular convenience for the act 

 itself. One must recognise this where pairing begins on the site 

 of the nest, and only comes to be upon it (the actual nest) as 

 the building (or rather heaping) progresses. In the case of the 

 Grebes it may appear otherwise, yet there are generally low and 

 flat shores in the vicinity of their breeding haunts ; and, more- 

 over, it is scarcely possible to imagine any species having actu- 

 ally to rear a structure in order to facilitate or make possible 

 this primary physical act, on which its continuance depends. 

 No bird, one must suppose, could have become aquatic beyond its 

 capacity for this functioning, under the new conditions, though 

 an acquired habit might have been transferred from the land to 

 the water. In the case of a non- aquatic bird, the whole surface of 

 the country, according to its habits, is open to it for this purpose, 

 whereas coition on the nest may be attended with more or less of 

 inconvenience. Thus Rooks have this habit, though it is not a 



