CUCKOO. 305 



creature. The cuckoo's legs, however, seemed very muscular, 

 and it appeared to feel about with its wings, which were abso- 

 lutely featherless, as with hands the 'spurious wing' (unusually 

 large in proportion) looking like a spread-out thumb. The most 

 singular thing of all was the direct purpose with which the blind 

 little monster made for the open side of the nest, the only part 

 where it could throw its burden down the bank. [The latter 

 remark has reference to the position of the nest below a heather 

 bush, on the declivity of a low abrupt bank, where the only 

 chance of dislodging the young birds was to eject them over the 

 side of the nest remote from its support upon the bank.] As 

 the young cuckoo was blind, it must have known the part of 

 the nest to choose by feeling from the inside that that part was 

 unsupported. 



Such being the facts, we have next to ask how they 

 are to be explained on the principles of evolution. At 

 first sight it seems that although the habit saves the bird 

 which practises it much time and trouble, and so is clearly 

 of benefit to the individual, it is not so clear how the in- 

 stinct is of benefit to the species ; for as cuckoos are not 

 social birds, and therefore cannot in any way depend on 

 mutual co-operation, it is difficult to see that this saving 

 of time and trouble to the individual can be of any use to 

 the species. But Jenner seems to have hit the right 

 cause in the concluding part of the above quotation. If 

 it is an advantage that the cuckoo should migrate early, 

 it clearly becomes an advantage, in order to admit of this, 

 that the habit should be formed of leaving her eggs for 

 other birds to incubate. At any rate, we have here a suffi- 

 ciently probable explanation of the raison d'etre of this 

 curious instinct ; and whether it is the true reason or the 

 only reason, we are justified in setting down the instinct 

 to the creating influence of natural selection. 



Mr. Darwin, in his l Origin of Species,' has some in- 

 teresting remarks to make on this subject. First, he 

 is informed by Dr. Merrell that the American cuckoo, 

 although as a rule following the ordinary custom of birds 

 in incubating her own eggs, nevertheless occasionally de- 

 posits them in the nests of other birds. 



Now let us suppose that the ancient progenitor of our Euro- 

 pean cuckoo had the habits of the American cuckoo, and that 



