A YOUNG CUCKOO 83 



(Dictionary of Birds : article CUCKO W), was 

 explicitly designed "to fit all round," and may well 

 cover mental reservations not appearing on the 

 surface. If I have ventured to take for examination 

 his statement of the case for assimilation rather than 

 another, it was because it was at once comprehensive 

 and comprehensible, qualities lacking in much that 

 has been written about the Cuckoo ; and because 

 its learned author's known sobriety of judgement 

 might be trusted to present only such points of the 

 case for assimilation as were likely to be worth 

 contending for. 



Although I have not entered into the question of 

 size in the above analyses, the survey can scarcely 

 be held to be complete even in its most obvious 

 aspects without reference to what is at least as 

 important a feature as colour or markings. I there- 

 fore append in the following table particulars showing 

 in what relationship the eggs of the foster-parents 

 stand to that of the Cuckoo in respect to size, taking 

 as the unit a Cuckoo's egg of average size, i *oo x 075 

 inch an average well within the mark. This table 

 shows the Cuckoo's egg to be about twice or three 

 times the bulk of the eggs of the birds most 

 frequently employed by it as foster-parents, whilst 

 in other cases it is four, and even five times as 

 large. One is bound to concede that the Cuckoo's 

 egg is remarkably small for so large a bird, but 

 may not one with equal justice urge that foster- 

 parents capable, according to the theory of assimila- 

 tion, of discriminating secondary characteristics such 

 as those of colour, should not be insensible to the 

 primary distinction of size ? 



