I90 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 tjrpe 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 comix and C. corone), Vv^hich, in the present -writer's 

 opinion, are only forms of the same dimorphic species, and, what is still 

 more wonderfid, 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 PiCARLE, 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, TiTKi- 

 midse, 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 Gavise, Limicolx, and Passeres, and in some 

 groups, as with the normal Gallinse, this seems to be enamelled or 

 much polished, but it is 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' Alcidse and the Accipitres. In 

 many of the Ratitx the surface is granulated and pitted in an 

 extraordinary manner,* and in a less degree the same feature is 



^ Zeitschr. /ilr wissensch. Zoologic, xv. pp. 1-31. 



2 Oi?. cit. xvii. pp. 480-524. 



'^ Op. cit. xviii. pp. 19-21, pp. 225-270, xix. pp. 322-348, xx. pp. 106-130, 

 xxi. pp. 330-335, xxx. pp. 69-77. A summary of these will be found in Journ. 

 fur Ornith. 1871, pp. 241-260, and the subject has been continued in the same 

 periodical for 1S72, 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 ns in Zool. Anzeigcr, 1885, pp. 413-415, 1886, pp. 555-569, 1887, pp. 292-296, 

 311-316. Some critical remarks by Dr. Kutter are contained in Journ. filr 

 Orn. 1877, pp. 396-423, 1878, pp. 300-348, 1880, j.p. 157-187'; and Orn. Certralbl. 

 1881, p. 68. 



* It is curious that Ostriches' eggs from North Africa are to be readUy dis- 

 tinguished from those from the Cape of Good Hope by their smooth ivory-like 



