A Theory of the Parasitic Habit of the Cuckoo. 65 



females do not pair in the strict sense ; there is no keeping 

 company, though the males are said to be passionate during 

 the breeding season. Nor is the female in its adult state 

 externally distinguishable from the male. 



(5.) The reproductive organs of both sexes are very small 

 for the size of the bird. There is said to be a diminished blood 

 supply. Little wonder, then, that the reproductive emotions 

 are in degree slightly developed. The sluggish parturition at 

 intervals of six to eight days is also striking and significant. 



(6.) The eggs are remarkably small. While the adult 

 cuckoo is some four times the size of an adult skylark, the 

 eggs are about the same size. The American cuckoo, which 

 is only occasionally parasitic, lays full-sized eggs. I know 

 that the size of the egg is not always proportionate to the size 

 of the bird. I am not saying that it should be. But I do 

 say that when a bird for constitutional reasons seems to 

 require all it can for itself, then it will have less to spare for 

 its reproductive sacrifice. To say that the small size of the 

 cuckoo's egg is " an adaptation in order to deceive the small 

 birds," seems to me to strain a theory to the breaking point. 

 (I shall not discuss the minor fact of the frequent similarity 

 between the colouring of the cuckoo's eggs and those of its 

 deluded victims. Darwinians explain this also by natural 

 selection, and speak of an inherited adaptation of egg-colour. 

 It seems legitimate to suggest, that in w^ays yet unintel- 

 ligible, the mother may be influenced during parturition by 

 the sight of objects [e.g., victim's eggs], which strongly 

 impress her. But this is entirely subsidiary.) 



(7.) It has been usual, in discussing beginnings, to take 



some cue from the young stages. It is noteworthy in this 



light to emphasise the jealous cruelty of the young form — 



a fit prophecy of the adult character. In the restlessness of 



rapid growth, the nestling expresses the constitution of the 



species in its selfish monopolising greed and insatiable 



appetite. Observations are recorded of the persistence of 



the cruel disposition into adolescence, though it usually 



wanes with the anatomical peculiarity of the back, not very 



long after birth. The young form at any rate exhibits the 



essential character of the species. 



VOL. X. E 



