204 Tlie World-Evidence. 



this country the cuckoos may not have been egg- 

 eating on a large scale, as they are now on a more 

 limited one ; the mobbing by small birds in return for 

 that injury remaining a witness of it. 



In New Zealand, too, there are instances of what 

 are called belated young birds not being able, for one 

 reason or another, to join in the migration. 



Here then, in the long-tailed New Zealand cuckoos, 

 we have an exact connecting link between the 

 American cuckoos and ours — a species which broods 

 its own eggs, but having done so, casts the young on 

 the care of others to be fed and tended. By this, the 

 perpetuation of the species seems to be just as fully 

 secured as by the more thoroughgoing tactics of Cuculus 

 canorus. But if so, Cuculus canorus takes on himself, 

 and has for long ages taken on himself, more labour 

 and effort, outside what we may. call the line of instinc- 

 tive action, than is really necessary to secure his end. 

 Or is it, then, that those cuckoos which have stopped 

 short of the complete parasitism of canorus, are but 

 yet on the way towards the point of perfection and 

 completeness to which he has attained ? Either this, 

 or it must be confessed that, in his perfection and 

 completeness, evolution is not justified of its children, 

 because we have here a machinery, so to say, most 

 complicated and involved — a machinery, which 

 through its very fineness, sometimes breaks down, 

 whereas, so far as we can learn, a less complicated 

 machinery — less affecting habit and function — has 

 been found to secure fully the end desired. If in 

 canorus you have the survival of the fit, on account 

 of distinctive and complete organisation and modifica- 

 tion of function, then in the New Zealand long-tails 



