404 THE ZOOLOGIST. 



This to me seems grotesque. The significance of a fact does not 

 lie only in its frequency, and Darwin himself would have been 

 very much hampered in his reasoning could he have drawn no 

 conclusion from cases of survival, reversion, or other anomaly, 

 till they had been proved to outnumber those in which no such 

 departure occurred. But, in the first place, there is another 

 class of assistance, besides that of nest-building, which the male 

 bird may render the female — incubation namely — and, in so far 

 as my theory (with which Miss Haviland does not appear to have 

 made herself entirely acquainted) is concerned, the one kind is 

 as pertinent to the argument as the other, since I suppose that 

 there was, first of all, the pairing-place, merely, which became the 

 nest by reason of the eggs being laid there and incubated 

 owing to their having been laid there — all this independently 

 of whether structure, even of the most primitive kind, had yet 

 supervened. Why, indeed, should the male bird help to incubate 

 eggs, not his own, any more than he should help to make a nest 

 for those eggs ? In my view, both these effects, as well as that of 

 true courting display action, grew out of the same ultimate cause, 

 viz., the sexual spur.* They are, in this connection, parts of one 

 whole, and therefore, for me, the inferences to be drawn from the 

 co-operation of the male, in either of these two functions, are 

 alike. It is, of course open to Miss Haviland to show the fallacy 

 of my inferences either in the one or the other case, or both, but 

 she must not rob me of half my material, whilst running away 

 from the other half, on the ground of its being exceptional — as 

 to which let us see. 



"What, then is the proportion of species in which the male 

 bird helps the female, either in building the nest or in incubating 

 the eggs, to those in which he shares in neither ? Here to some 

 extent is the answer. Out of 212 species of birds that are 

 mentioned in ' The British Bird Book ' as breeding, either 

 habitually or occasionally, in these Islands, the details on this 

 head, given in the "Classified Notes," are as follows: In 63 

 species out of the whole 212, the male bird assists the female 

 both in nidification and incubation. In 13 species he assists 

 her in nidification, but whether he does in incubation also is 



* Incubation, however, more incidentally and less genetically than the 

 other two. See post, p. 408 (11) and (12; with marginal references. 



