190 EGGS 
investigations carried on by Drs. Landois! and Rudolf Blasius,? he 
brought out a series of remarkable papers? in which he arrived at 
the conclusion that a well-defined type of shell-structure belongs to 
certain Families of birds, and is easily recognized under the micro- 
scope. In some cases, as in the eggs of certain SWANS and GEESE 
(Cygnus olor and C. musicus, Anser cinereus and A. segetum) even 
specific differences are apparent; but more than this, differences 
of the same kind are observable in the eggs of the Grey and Black 
Crows (Corvus corniz and C. corone), which, in the present writer’s 
opinion, are only forms of the same dimorphic species, and, what is still 
more wonderful, the eggs of the hybrids or mongrels between these 
two forms are recognizable under the microscope by the structure 
of the shell, while yet most extraordinary is the general conclusion 
that the egg laid by a bird mated with a male of a different species 
is recognizable from one laid by the same bird when paired with a 
male of her own. The bearing of these researches on classification 
generally is of considerable importance and must be taken into 
account by all future taxonomers. Here we cannot enter into 
details, it must suffice to remark that the grain of the shell is some- 
times so fine that the surface is glossy, and this is the case with a 
large number of PICARL&, where it is also quite colourless and the 
contents of their eggs seen through the semi-transparent shell give 
an opalescence of great beauty; but among the TinAmous, Tina- 
midz, colour is invariably present and their opaque eggs present 
the appearance of more or less globular balls of highly-burnished 
metal or glazed porcelain. Most birds lay eggs with a smooth shell, 
such as nearly all the Gavixw, Limicolx, and Passeres, and in some 
groups, as with the normal Gallinz, this seems to be enamelled or 
much polished, but itis still very different from the brilliant surface 
of those just mentioned, and nothing like a definite line can be 
drawn between their structure and that in which the substance is 
dull and uniform, as among the Alcidw and the Accipitres. In 
many of the Ratity the surface is granulated and pitted in an 
extraordinary manner,* and in a less degree the same feature is 
1 Zeitschr. fiir wissensch. Zoologie, xv. pp. 1-81. 
2 Op. cit. xvii. pp. 480-524. 
5 Op. cit. xviii. pp. 19-21, pp. 225-270, xix. pp. 322-348, xx. pp. 106-130, 
xxi. pp. 830-335, xxx. pp. 69-77. A summary of these will be found in Jowrn. 
fiir Ornith. 1871, pp. 241-260, and the subject has been continued in the same 
periodical for 1872, pp. 321-332, 1874, pp. 1-26, 1879, pp. 525-761, 1880, pp. 
341-346, 1881, pp. 334-336, 1882, pp. 129-161, 225-315, 1885, pp. 165-178; as 
well as in Zool. Anzeiger, 1885, pp. 413-415, 1886, pp. 555-569, 1887, pp. 292-296, 
311-316. Some critical remarks by Dr. Kutter are contained in Journ. fiir 
Orn. 1877, pp. 896-423, 1878, pp. 300-348, 1880, pp. 157-187; and Orn. Centralbl. 
1881, p. 68. 
4 It is curious that Ostriches’ eggs from North Africa are to be readily dis- 
tinguished from those from the Cape of Good Hope by their smooth ivory-like 
