19 1 7- J Letters, Extracts^ and Notes. 635 



the branches of trees or elsewhere^ and doled them out as 

 required ! The evidence on behalf of this theory (p. 210) 

 is so extremely flimsy, and contrary to the experience of all 

 who have witnessed the oviposition of the Cuckoo, that it 

 scarcely needs refutation. 



It seems hardly fair to pass judgment on Dr. Key's claim 

 to be able to assign eggs to specific females on the grounds 

 stated on pp. 195-197. It is of course perfectly true that 

 the Tree-Sparrow lays eggs of diff'erent types in the same 

 clutch, but it is equally true that the eggs of such species 

 as the Tree-Pipit and the Red-backed Shrike are almost 

 always true to type in the clutch. Moreover, no account 

 is taken of the fact (which is admitted on p. 216) that 

 each Cuckoo deposits her eggs in a restricted locality. 

 To separate the eggs of two or three pairs of Eed-backed 

 Shrikes or Tree-Pipits from one district is not as a rule 

 at all a difficult task. To assign each egg even from a small 

 colony of Guillemots in two consecutive years is not in any 

 way a parallel case, although it may frequently be done with 

 absolute certainty in the case of individual birds. The 

 thirty-four hen Cuckoos to Avhich Dr. Rey refers in the 

 country round Leipzig, did not range over the same ground, 

 but had in each case a special district, although no doubt 

 the boundaries of adjacent hens overlapped from time to 

 time. Having had the advantage of inspecting Dr. Rey's 

 wonderful series, I unhesitatingly assert that though occa- 

 sionally he may have been misled by the similarity in the 

 eggs of two females in adjoining areas, his claim would be 

 upheld by any unbiassed judge in the vast majority of cases. 

 Inferences drawn from the necessarily brief descriptions of 

 the type or raeasureraents alone apart from colour and 

 markings are necessarily fallacious. No reference is made 

 to the remarkable fact that the variability of British Cuckoos^ 

 eggs is considerably less than that of Continental specimens. 

 Particulars of the supposed blue Cuckooes egg referred to by 

 Dr. A. Gr. Butler {antea, p. 459) as having been taken by the 

 late Mr. W. Borrer will be found in the ' Birds of Sussex," 

 p. 167, but there is no evidence in this or other supposed 



