ORTHOGENESIS 349 



That the original progenitors of our cuckoo when they began to lay 

 their eggs in other nests acted by reflection and with design. We have 

 no certain knowledge that the cuckoo does not at the present day lay its 

 eggs in other birds' nests after conscious reflection. We do not know, 

 therefore, how far this action is due to intelligence. That it is not 

 a perfect instinct is shown by the fact above-mentioned, that our 

 cuckoo at times sits on her own eggs and feeds her young ; and it is 

 especially noteworthy that it builds no nest for the purpose. 



This is, of course, disputed. Brehm ascribes the statement to a 

 confusion of the cuckoo with the goatsucker, but Darwin himself 

 regards it as satisfactorily proved. But if the fact is considered 

 unproved, the other fact that the American cuckoo sometimes incubates 

 its own eggs, sometimes lays them in other birds' nests, and the 

 a priori assumption that the instinct of our cuckoo has been gradually 

 developed, imply that there was a time when it still occasionally incu- 

 bated its own eggs, as conversely the American cuckoo now only occa- 

 sionally lays its eggs in other nests. Who can prove that reflection 

 did not underlie this difference of action, determining it according to 

 the different conditions? For the cuckoo certainly shows reflection in 

 its choice of nests in which to lay its eggs, and in many other actions. 

 But whether our cuckoo acts at the present day from pure instinct 

 or still by reflection even assuming the first it is, I believe, necessary, 

 in order to explain the instinct, to start from the supposition that it 

 has arisen by the inheritance of habit originally intelligent. The 

 conditions of life of the bird enable us to understand easily enough 

 the ultimate causes of the habit. 



The cuckoo lives the life of a vagabond. It wanders about rest- 

 lessly ; in the first place, it remains with us only a few months, from 

 April to August; secondly, even in the region where it settles here it 

 has no permanent station, it wanders now in one direction, now in 

 another. This restlessness is caused by its insatiable appetite and 

 sexual desires. It is ever seeking food and mates. Its food consists 

 principally of caterpillars, especially those which, like Gastropacha pini, 

 occur only here and there in great abundance. The cuckoo must there- 

 fore move about in order to satisfy its need of food. When it has 

 found a swarm of caterpillars it revels in excess, and its sexual require- 

 ments are increased. 



" Speaking of the long duration of the egg-producing season 

 in the case of the cuckoo, he says : 



It was probably ultimately determined by the irregular habits of 

 life, the irregular, but on the whole extraordinarily abundant con- 

 sumption of food, and the varying demands of sexual excitement. Thus 

 our domestic hens have been brought by continued high-feeding to lay 

 eggs throughout the greatest part of the year, and to receive the male 



