256 



THE EVOLUTION OF SEX. 



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. It is true that the size of an egg is not always 

 proportionate to the size of the bird; but it is reasonable to believe 

 that when a bird for constitutional conditions seems to require all it 

 can for itself, then it will have less to spare for its reproductive sacri- 

 fice. To say that the small size of the cuckoo's egg is " an adaptation 

 in order to deceive the small birds," seems to strain the natural selec- 

 tion theory to the breaking point. 



7. It has been usual in discussing beginnings to take some cue 

 from the young stages. It is noteworthy, in this light, to emphasize 

 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 monopolizing 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. 



8. Some corroboration is obtained from the character of the 

 American cuckoo. There seems no doubt that it is occasionally para- 

 sitic, and it is interesting to note that observers speak of its unnaturally 

 careless indifference for the fate of its young. The character, in fact, 

 is less markedly evil; the occasional parasitism is just as intelligible as 

 the occasional " reversion " of our cuckoo to ancestral habits, even in 

 some cases to apparent affection for the young. 



9. In the cowbirds, again, where the habit occurs in different 

 species in different degrees of perfection (if the term be admissible), 

 the character is strikingly immoral. In one species {Molothrus cadius), 

 a nest may be simply stolen, or the rightful nestlings may be thrown 

 out, or actual parasitism may occur as an exception. In M. canaricnsis y 

 the eggs may be dropped on the bare ground, or fifteen to twenty 

 from different parents may be lazily and of course fatally huddled 

 together in one nest. Two cuckoo-eggs are sometimes found in one 

 nest. In M. pecoris, which is polygamous, the crime has been evolved, 

 and the habit is that of our cuckoo, one egg being laid in each foster- 

 nest. The important point is the general immorality and reproductive 



