122 CUCKOW 



in illustration of his paper, and, however the thing may be accounted 

 for, it seems impossible to resist, save on one supposition, the force of 

 the testimony these specimens afford. This one supposition is that 

 the eggs have been wrongly ascribed to the Cuckow, and that they 

 are only exceptionally large examples of the eggs of the birds in the 

 nests of which they were found, for it cannot be gainsaid that some 

 such abnormal examples are occasionally to be met "\\"ith. But it is 

 well known that abnormally-large eggs are not only often deficient 

 in depth of colour, but still more often in stoutness of shell. 

 Applying these rough criteria to Dr. Baldamus's series, most of the 

 specimens stand the test very well, and, though no doubt more 

 precise and delicate examination, than any to which they seem to 

 have been submitted, were desirable, there are some other consider- 

 ations to be ui^ged. For instance, Herr Braune, a forester at Greiz 

 in the principality of Reuss {Naumannia, 1853, pp. 307, 313), shot 

 a hen Cuckow as she was leaving the nest of an Icterine Warbler 

 {Hypolais iderina). In the o\dduct of this Cuckow he found an egg 

 coloured very like that of the Warbler, and on looking into the 

 nest he found there an exactly similar egg, which there can be no 

 reasonable doubt had just been laid by that very Cuckow. More- 

 over, Herr Grunack {Jour, fur Orn. 1873, p. 454) has since found 

 one of the most abnormally-coloured specimens, quite unlike the 

 ordinary egg of the Cuckow, to contain an embryo so fully formed 

 as to shew the characteristic zygodactyl feet of the bird, thus 

 proAdng unquestionably its parentage. Now these being both of 

 them extreme cases, Dr. Baldamus may fairly claim attention to his 

 assertion ; for short of absolutely disbelieving his word we must 

 admit that he has ground for it. On the other hand, we must 

 bear in mind the numerous instances in which not the least simi- 

 larity can be traced — as in the not uncommon case of the Hedge- 

 Sparrow already mentioned, and if we attempt any explanatory 

 hypothesis it must be one that will fit all round. Such a one then 

 seems to be this. We know that certain kinds of birds resent 

 interference mth their nests much less than others, and among 

 them it may be asserted that the Hedge-Sparrow will patiently 

 submit to various experiments. She will brood with complacency 

 the egg of a Redbreast (Erithacus rubeada), so unlike her own, and 

 for aught we know to the contrary may even be colour-blind. In 

 the case of such a species there would be no need of anything 

 further to insure success — the terror of the nest-OAvner at seeing her 

 home invaded by a Hawk-like giant, and some of her treasui'es 

 tossed out, would be enough to stir her motherly feelings so deeply 

 that she would without misgiving, if not -with joy that something 

 had been spared to her, resume the duty of incubation so soon as 

 the danger was past. But "SAdth other species it may be, nay doubt- 

 less it is, different. Here assimilation of the introduced egg to 



