I30 A HISTORY QF BIRDS 



like her own. The most probable explanation is that which has 

 been formulated by the late Professor Newton— though he does 

 not claim the discovery as wholly his own — who suggests that 

 the Cuckoo has split up into a number of distinct " gens ". Thus 

 he recognises Robin Cuckoos, Meadow-pipit Cuckoos, Wagtail 

 Cuckoos, Reed-warbler Cuckoos, and so on — Cuckoo-types 

 whose eggs resemble the several species just enumerated. This 

 formation of Cuckoo " gens " has, he suggests, been brought about 

 by selection. When the Cuckoo first began to shirk the duties of 

 incubation by dropping its eggs into the nests of other birds, 

 only those were hatched which sufficiently matched those of 

 the dupe, the others being ejected from the nests by the owners 

 thereof. A further process of selection took place, moreover, if, 

 on hatching, the food of the dupe proved unsuitable to the 

 needs of the foundling. Thus, it would come about that 

 female Cuckoos reared in Robins or Wagtails' nests would seek 

 the nests of these birds in which, in turn, to lay their own eggs. 

 The probability of this explanation of the evolution of the 

 resemblance between the eggs of the Cuckoo and those of its 

 host has recently been exhaustively investigated by Mr. 

 Oswald Latter, and though he at first felt sceptical about the 

 matter, he has come to the conclusion, after examining many 

 hundreds of eggs, that the theory is well founded. 



A most serious objection, however, it has been urged, to 

 the stability of this theory is the certainty that female " Robin 

 Cuckoos " must frequently mate with male " Wagtail Cuckoos," 

 and so on, and that this being so we must assume that the 

 inherited habits and characters of every female Cuckoo must 

 follow only the female line of descent. But this objection is 

 based on a confusion of the facts of the case. It appears to be 

 forgotten that these " Robin Cuckoos " and " Wagtail Cuckoos " 

 are not hybrids between the foster-parent and the Cuckoo. 

 What the female Cuckoo has inherited is the instinct to seek 

 out, whenever possible, nests of birds of the species by which it 

 was reared. And there is nothing more wonderful in this than 

 in the remarkable inherited instincts of many female insects 

 which make peculiar provisions for their oiTspring : in the case 

 of the Cuckoo we are dealing with inherited instinct prompted 

 by memory. 



That the Cuckoo must keep a careful watch on birds likely 



