1 88 EGGS 



think that Oorhodeine is in some way or othei^ closely related to 

 Cruentine, being probably derived from the red colouring-matter 

 of the blood by some unknown process of secretion, and likewise that 

 there is some chemical relation between the Oocyans and the bile. 



It was remarked by Hewitson in 1838 {Brit. Oology, Introd. p. 8), 

 and perhaps he was not the first to make the observation, that 

 the eggs of many if not of most birds which breed in holes, or 

 even in covered nests, are of an uniform white ; but the number of 

 exceptions is so great, that no general rule can be laid down to this 

 effect. Conversely, the numbei- of birds which lay purely white 

 eggs in open nests — the multitudinous species of Pigeon being 

 notorious instances of the fact^ — is also large, and in some respects 

 quite independent of their taxonomic relations, as, for example, the 

 Little Bittern among the Ardeidx, the Virginian Quail among 

 the so-called " Odontophorinse," and again among the Gallinse, even 

 the Common Fowl, though some of its breeds, perhaps acted upon by 

 what is known as " reversion," lay coloured eggs. The eggs of Owls 

 are always white, whether the species be one that breeds in holes, 

 on the bare ground, or in an open nest in a tree. The egg of the 

 G OS-Hawk is white, but that of its small relative the Sparrow- 

 Hawk is always blotched, and sometimes richly, with pigment, the 

 nest of both being built precisely in the same kind of position, — 

 but it would be almost endless to cite similar cases. To account 

 for some, at least, of these anomalies, an ingenious hypothesis has 

 been set forth by Dr. M'Aldome," starting on the assumption " that 

 the pigmentaiy coat on birds' eggs came into existence at a very 

 early period in their life-history, and existed in the eggs of the 

 progenitors of all the extant species." It is further taken as proved 

 that the pigments being " unstable and variable " makes " the pro- 

 cess of change and decolorization a simple one ; and that its 

 primary use is for protection from the solar rays, but that it 

 afterwards becomes modified for concealment." Finally, it is main- 

 tained " that eggs acquire a highly developed pigmentary layer, 

 or lose their pigment entirely, according to whether they are ex- 

 posed to the full glare of the sun or laid in situations inaccessible 

 to its rays, and that the intermediate degrees of coloration are in 

 direct ratio to the amount of light to which the eggs are exposed.^ 



^ Of course, Columha livia, and its allies C. schimperi and C. intermedia, 

 usually breed in caves, and C. cenas generally though not always places its nest 

 under cover, but these seem to be the only exceptions in a Family comprising 

 some 350 species. 



- Observations on the Development and the Decay of the Pigment Layer in 

 Birds' Eggs, Joimi. Anat. and Physiol, xx. (1886), pp. 225-237. 



^ It is to be observed that the author bases his h.ypothesis on a study of the 

 eggs of British birds only. Considering that in most respects the most instruc- 

 tive forms of the Class do not belong to our own limited fauna, allowance 

 must be made for the imperfect information whence his results are drawn. 



