INSTINCT 859 



cuckoo, which are spoken of as necessarily co-ordinated. 

 But in all cases speculation on an instinct known to us 

 only in a single species is useless, for we have hitherto 

 had no facts to guide us. Until recently the instincts of 

 the European and of the non-parasitic American cuckoo 

 alone were known; now, owing to Mr, Eamsay's observa- 

 tions, we have learned sometiaing about three Australian 

 species which lay their eggs in other birds' nests. The 

 chief points to be referred to are three: first, that the 

 common cuckoo, with rare exceptions, lays only one egg 

 in a nest, so that the large and voracious young bird 

 receives ample food. Secondly, that the eggs are remark- 

 ably small, not exceeding those of the skylark — a bird 

 about one-fourth as large as the cuckoo. That the small 

 size of the egg is a real case of adaptation we may infer 

 from the fact of the non-parasitic American cuckoo lay- 

 ing full-sized eggs. Thirdly, that the young cuckoo, soon 

 after birth, has the instinct, the strength, and a properly 

 shaped back for ejecting its foster-brothers, which then 

 perish from cold and hunger. This has been boldly 

 sailed a beneficent arrangement, in order that the young 

 buckoo may get sufficient food, and that its foster broth- 

 ers may perish before they had acquired much feeling! 

 Turning now to the Australian species; though these 

 )irds generally lay only one egg in a nest, it is not rare 

 o find two and even three eggs in the same nest. In 

 he Bronze cuckoo the eggs vary greatly in size, from 

 ight to ten lines in length. Now if it had been of an 

 jii Advantage to this species to have laid eggs even smaller 

 [ban those now laid, so as to have deceived certain foster- 

 (j Barents, or, as is more probable, to have been hatched 

 jilithin a shorter period (for it is asserted that there is a 



