INSTINCT 857 



duce inherited mental changes; in other cases, compulsory 

 habit has done nothing, and all has been the result of 

 ■ selection, pursued both methodically and unconsciously: 

 but in most cases habit and selection have probably 

 concurred. 



Special Instincts 



We shall, perhaps, best understand how instincts in 

 a state of nature have become modified by selection, by 

 considering a few cases. I will select only three — namely, 

 the instinct which leads the cuckoo to lay her eggs in 

 other birds' nests; the slave-making instinct of certain 

 ants; and the cell-making power of the hive-bee. These 

 two latter instincts have generally and justly been ranked 

 by naturalists as the most wonderful of all known 

 instincts. 



Instincts of the Cuchoo. — It is supposed by some natu- 

 ralists that the more immediate cause of the instinct of 

 the cuckoo is that she lays her eggs, not daily, but at 

 ntervals of two or three days; so that, if she were to 

 nake her own nest and sit on her own eggs, those first 

 aid would have to be left for some time unincubated, or 

 here would be eggs and young birds of different ages in 

 he same nest. If this were the case, the process of 

 aying and hatching might be inconveniently long, more 

 specially as she migrates at a very early period; and 

 !he first hatched young would probably have to be fed 

 y the male alone. But the American cuckoo is in this 

 ectiljredicament ; for she makes her own nest, and has eggs 

 itiiliind young successively hatched, all at the same time. 

 fri||i; has been both asserted and denied that the American 

 ickoo occasionally lays her eggs in other birds' nests; 

 ^fiiit I have lately heard from Dr. Merrell of Iowa that 



