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 with. 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 urged. For instance, Herr Braune, a forester at Greiz 
in the principality of Reuss (Wawmannia, 1853, pp. 307, 313), shot 
a hen Cuckow as she was leaving the nest of an Icterine Warbler 
(Hypolais icterina). In the oviduct 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. fiir 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 
proving 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 with 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 (Hrithacus rubecula), 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-owner at seeing her 
home invaded by a Hawk-like giant, and some of her treasures 
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 with other species it may be, nay doubt- 
less it is, different. Here assimilation of the introduced egg to 
