A SETTLED QUESTION 103 



indeed, he might prove the thing in a moment, 

 but not the other way. For instance, if he were 

 to see a cuckoo lay an egg, and if that cuckoo 

 cuckooed, the assumption that the male bird alone 

 can do so would be, at once, disproved ; but if it 

 'merely did not cuckoo, the question would lie open, 

 as before. The chance, however, of making such 

 an observation as this is an exceedingly small one. 

 We must think of some other that would be equally 

 a test. Certain activities may bring the sexes to- 

 gether, by themselves, but nidification, incubation, 

 and the rearing of the young, are all non-existent 

 in the case of the cuckoo. The problem cannot be 

 solved in the way that I have solved it, with the 

 nightjar. There is, however, the nuptial rite, and 

 if we could see this performed, and were able to 

 keep the sexes distinct, for some time afterwards, 

 something, perhaps, might be got at. Let us sup- 

 pose, then, that two cuckoos are observed under 

 these circumstances, and that the male, only, cuckoos. 

 Here, again, this would be mere negative evidence, 

 in regard to the point in dispute. Either both 

 the birds, or the female only, must cuckoo, or else 

 the observation, so difficult to make, must be re- 

 peated indefinitely, and, moreover, each time that 

 neither bird cuckooed — which might very often be 

 the case — nothing whatever would have been gained. 

 This is the view I take of the difficulties which 

 lie in the way of really knowing whether the 

 male and female cuckoo utter distinct notes. Short 

 of the test I have suggested, one can only, 

 I believe, come to a conclusion by begging 

 the question — which has accordingly been done. 



