3508 The Zoologist— May, 1873. 



they were unpacked, it appeared that there were two more speci- 

 mens of the egg of a large North-African cuckow {Oxyloplms 

 glandarius) than I had been led by him to expect. On examina- 

 tion, I found that the first two eggs of this species which had been 

 obtained by him so much resembled eggs of the magpie of the 

 country [Pica maurilanica), in the nests of which they had been 

 found, that, skilful oologist as he was, they had passed, even to his 

 practised though unsuspecting eye, as those of the latter bird. 

 Had I known then of Salerno's words, I should have exclaimed 

 with him, " c'est une chose incomprehensible ! " 



Having said thus much, and believing as I do the Doctor to be 

 partly justified in the carefully-worded enunciation of what he calls 

 a " Law of Nature," I must now declare that it is only " approxi- 

 mately" and by no means universally ixuQ that the cuckow's egg is 

 coloured like those of the victims of her imposition. Increase as 

 we may, by renewed observations, the number of cases which bear 

 in favour of his theory, yet, as almost every bird's-nesting boy 

 knows, the instances in which we cannot, even by dint of straining 

 our fancy, see resemblances where none exist, are still so 

 numerous as to preclude me from believing in the generality of the 

 practice imputed to the cuckow. In proof of this I have only to 

 mention the many eggs of that bird which are yearly found in nests 

 of the hedge-sparrow in this country, without ever bearing the 

 faintest similarity to its well-known green-blue eggs. One may 

 grant that an ordinary English cuckow's egg will pass well enough, 

 in the eyes of the dupe, for that of a titlark, a pied wagtail, or a 

 recd-wren, which, according to my experience, are the most common 

 foster-parents of the cuckow in this country ; and indeed one may 

 say, perhaps, that such an egg is a compromise between the three, 

 or a resultant, perhaps, of three opposing forces; but any likeness 

 between the hedge-sparrow's^ egg and the cuckow's, so often found 

 alongside of it, or in its place, is not to be traced by the most 

 fertile imagination. We must keep therefore strictly to the letter 

 of the law laid down by Dr. Baldamus, and the practice imputed 

 to the cuckow is not universally but only "approximately" fol- 

 lowed. 



Now, is it possible to give a satisfactory explanation of the 

 process by which the facts alleged are produced ? Dr. Baldamus 

 assigns none. He lays down a number of aphorisms, most of 

 which are very interesting, and, I believe, true ; but they do not 



