252 SPECIAL INSTINCTS, 



cuckoo, with rare exceptions, lays only one Qgg in a nest, 

 60 that the large and voracious young bird receives ample 

 food. Secondly, that the eggs are remarkably small, not 

 exceeding those of the skylark — a bird about one-fourth as 

 large as the cuckoo. That the small size of the Qgg is a 

 real case of adaptation we may infer from the fact of the 

 uou-parasitic American cuckoo laying full-sized eggs. 

 Thirdly, that the young cuckoo, soon after birth, has the 

 instiuct, the strength and a properly shaped back for eject- 

 ing its foster-brothers, which then perish from cold and 

 hunger. This has been boldly called a beneficent arrange- 

 ment, in order that the young cuckoo may get sufficient 

 food, and that its foster-brothers may perish before they 

 nad acquired much feeling! 



Turning now to the Australian species: though these 

 birds generally lay only one Qgg in a nest, it is not rare to find 

 two and even three eggs in the same nest. In the bronze 

 cuckoo the eggs vary greatly in size, from eight to ten 

 lines in length. Now, if it had been of an advantage to 

 this species to have laid eggs even smaller than those now 

 laid, so as to have deceived certain foster-parents, or, as is 

 more probable, to have been hatched within a shorter 

 period (for it is asserted that there is a relation between 

 the size of eggs and the period of their incubation), then 

 there is no diffi.culty in believing that a race or species 

 might have been formed which would have laid smaller and 

 smaller eggs; for these would have been more safely hatched 

 and reared. Mr. Eamsav remarks that two of the Australian 

 cuckoos, when they lay their eggs in an open nest, mani- 

 fest a decided preference for nests containing eggs similar 

 in color to their own. The European species apparently 

 manifests some tendency toward a similar instinct, but not 

 rarely departs from it, as is shown by her laying her dull 

 and pale-colored eggs in the nest of the hedge-warbler 

 with bright greenish-blue eggs. Had our cuckoo invari- 

 ably displayed the above instinct, it would assuredly have 

 been added to those which it is assumed must all have 

 been acquired together. The eggs of the Australian bronze 

 cuckoo vary, according to Mr. Ramsay, to an extraordinary 

 degree in color; so that in this respect, as well as in size, 

 natural selection might have secured and fixed any advan- 

 tageous variation. 



