240 MR J, B. DOBBIE ON 
parasitic Cuckoos, that of Cuculus canorus being an out- 
standing example. This is just what might be expected, for 
our Cuckoo is a parasite upon birds much smaller than itself. 
But, strangely enough, in the case of another parasite, Molo- 
thrus bonariensis, we meet with diametrically opposite results. 
Here we have a bird whose egg is relatively very large indeed, 
and yet its dupes are, with hardly an exception, even smaller 
than itself! How are we to explain an anomaly so striking 
as this? Had the parasitical habits acquired by the bird 
rendered necessary any modification in the size of the egg, 
we should naturally have expected, as has occurred in the 
case of Cuculus canorus, a slight decrease rather than a 
remarkable increase. Mr W. H. Hudson, who has so carefully 
studied and so ably described the procreant habits of this 
and other South American Cowbirds, affirms that the egg of 
Molothrus bonariensis, despite its comparatively large size, 
hatches in 114 days, while the eggs of other small birds, 
such as those of its dupes, require fourteen to sixteen days, 
and by this means, therefore, it would appear, the species is 
preserved. 
5. TEXTURE OF SURFACE. 
The texture of shell, as Dr Rey has pointed out, depends 
upon structural conditions. “It stands in direct relation 
to the forms and abundance of certain glands in the womb, 
the so-called uterine glands, and is in its complicated form 
a criterion of the exact differentiation of many genera and 
families—even of those whose eggs are in other respects 
similar.” By the texture alone it is possible for the oologist 
to identify eggs which are, in other external respects, 
indistinguishable. For example, it is quite a simple matter 
to distinguish, with the aid of a lens, between eggs of an 
Owl and those of a Roller, though both are of an uniform 
white, so strikingly unlike are they in texture. Most 
wonderful is the remarkable fact, as recorded by Prof. 
Newton, that the eggs of the Carrion and Hooded Crows are 
readily distinguishable under the microscope by the struc- 
ture of the shell; and more wonderful still is “the general 
conclusion that the egg laid by a bird mated with a male of 
