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amongst which it has been placed. Mr. C. Sachse, a most careful observer and field-naturalist, 

 writes to me from Altenkirchen, near Coblentz, as follows : — " For many years I have taken note 

 of the breeding-habits of the Cuckoo, and corresponded much with Dr. Baldamus on the subject, 

 and have definitely arrived at the conclusion that the same female Cuckoo lays similarly-coloured 

 eggs. In 1866 I found a Cuckoo's egg with four eggs of Turdus merula, which was coloured 

 very abnormally, and strikingly like the egg of Emberiza miliaria; and fourteen days later I 

 found in the immediate neighbourhood a similarly coloured egg in the nest of Erythacus rubecula. 

 As these eggs were very abnormally coloured, and the Cuckoo is not a common bird here, I may 

 judge with certainty that the same female laid them. I noticed a similar case last year, when I 

 found similarly-coloured Cuckoo's eggs in the nests of the Chiffchaff and Willow- Wren ; and 

 Baldamus has often made like observations. I have also found very abnormally-coloured eggs in 

 the nests of the Warblers, which greatly resembled the eggs of the foster-parents ; still I cannot 

 agree with Dr. Baldamus's theory that the Cuckoo is able to assimilate her egg to those of the 

 species in whose nest she deposits it, because I have so frequently found them not resembling 

 the eggs of the foster-parent." I may here remark, however, that Dr. Baldamus does not state 

 that the Cuckoo can assimilate her eggs to those of the foster-parent, but merely says that she 

 usually deposits her egg with those of some species which it most nearly resembles. 



Professor Newton, in his article on the Cuckoo in the ninth edition of the ' Encyclopaedia 

 Britannica' (vol. vi. pp. 685-687), has given the latest resume of what has been written on the 

 peculiar breeding-habits of the present species ; and, referring to what Dr. Baldamus has written 

 on the subject, he remarks that " there can hardly be a doubt as to the truth of Dr. Baldamus's 

 theory (the only theory, by the way, he has put forth) as to the object of the assimilation being 

 to render the Cuckow's egg ' less easily recognized by the foster-parents as a substituted one.' 

 But in this place it is especially desirable to point out that there is 'not the slightest ground for 

 imagining that the Cuckow or any other bird can voluntarily influence the colour of the egg she 

 is about to lay. Over that she can have no control; but its destination she can determine. It 

 would seem also impossible that a Cuckow, having laid an egg, should look at it and then decide 

 from its appearance in what bird's nest she should put it. That the colour of an egg-shell can be 

 in some mysterious way affected by the action of external objects on the perceptive faculties of 

 the mother is a notion too wild to be seriously entertained. Consequently only one explanation 

 of the facts can here be suggested. Every one who has sufficiently studied the habits of animals 

 will admit the tendency of some of those habits to become hereditary. That there is a reasonable 

 probability of each Cuckow most commonly putting her eggs in the nest of the same species of 

 bird, and of this habit being transmitted to her posterity, does not seem to be a very violent 

 supposition. Without attributing any wonderful sagacity to her, it does not seem unlikely that 

 the Cuckow which had once successfully foisted her egg on a Reed- Wren or a Titlark should 

 again seek for another Beed-Wren's or another Titlark's nest (as the case may be) when she had 

 another egg to dispose of, and that she should continue her practice from one season to another. 

 It stands on record (Zool. 1873, p. 3648) that a pair of Wagtails built their nest for eight or 

 nine years running in almost exactly the same spot, and that in each of those years "they 

 fostered a young Cuckow, while many other cases of like kind, though not perhaps established 

 on authority so good, are believed to have happened. Such a habit could hardly fail to become 

 hereditary, so that the daughter of a Cuckow, which always put her egg into a Reed- Wren's, 



