The Zoologist — April, 1868. 1161 



same day two cuckoo's eggs, coloured exactly alike, of the type of the 

 eggs of Sylvia cinerea, in two nests of that bird, in the district of that 

 pair, the cock bird of which attracted my whole attention by his 

 peculiar cry. Both eggs undoubtedly belonged to the same hen 

 bird. After about eight or nine days, a boy, whom I had commissioned 

 to search for nests in the district which T pointed out, brought me 

 a third egg, exactly similar, together with the nest and eggs of 

 S. hortensis : all three eggs are in my collection, and are not to be 

 distinguished from one another. We may with confidence assert that 

 this third egg also belongs to the same hen, or rather pair, in whose 

 district the boy had found it. 



Thus all experience hitherto made declares for the assertion that 

 every hen cuckoo lays only eggs of one colouring, and consequently 

 (as a general rule) lays only in the nests of one species. 



" All experience hitherto made," I say, including even the exceptions 

 to the rule. Yes, indeed, for it is just here that these find the only 

 satisfactory explanation. We repeat once more, so striking an 

 appearance of the cuckoo's eggs, agreeing with the very various 

 colouring of the warbler's eggs, cannot be accidental or without pur- 

 pose. Moreover, it is easy enough to see the purpose which Nature 

 has in view herein. Most certainly, too, does she attain that purpose, 

 by securing and facilitating the continuance of the species, through 

 the circumstances, once and for some good reasons firmly established, 

 which forbid the cuckoo to hatch and rear her own young. She 

 attains this purpose in the way above mentioned, perhaps also by 

 some other means. In short, we think the case to be this : every pair, 

 or rather each individual cuckoo, is endowed with the instinct to lay 

 its eggs in the nests of some one species of birds which are fit to act 

 the part of foster-parents; so in order that these latter may the less 

 readily observe the strange egg it is found to be of similar colouring 

 to their own ; and perhaps for the same reasons it is also so dispropor- 

 tionably small. Then every pair of cuckoos seeks its old district, or 

 that spot where it breeds, just as all other birds do. Here (as a general 

 rule) it finds those species of warblers which it requires for its peculiar 

 circumstances, but certainly not always in the necessary numbers, or 

 perhaps breeding earlier or later than its six to eight weeks' time for 

 laying ["legezeit"] lasts. It will therefore be unable to find for each 

 of its eggs a fitting nest of that species to which it was prepared to 

 entrust it, and to which it was used, and so it finds itself obliged to 



SECOND SERIES — VOL. III. T 



