530 Mr. C. F. M. Swynnerton on 



Eggs," Journ. Anat. & Physiol, xx. 1886, pp. 225-227). 

 Dr. McAldowie, starting on- the assumption " that the 

 pigmentary coat on birds' eggs came into existence at a very 

 early period . . . and existed in the eggs of the progenitors 

 of all the extant species/' suggests " that its primary use is 

 for protection from the solar rays, but that/' the pigment 

 being " unstable and variable " and change therefore easy, 

 " it afterwards became modified for concealment." Finally, 

 " eggs acquire a highly developed pigmentary layer, or lose 

 their pigment entirely, according to whether they are 

 exposed to the full glare of the sun or laid in situations 

 inaccessible to its rays, and . . . the intermediate degrees of 

 coloration are in direct ratio to the amount of light to which 

 the eggs are exposed." 



The theory might be regarded as receiving support from 

 the fact that a considerable number of white eggs are laid 

 in holes, and from such instances of apparent paling as those 

 of the Jackdaw and Puffin. But it is interesting to note 

 that there is no such additional pigmentation of tropical eggs 

 as there is, apparently, of the skins of tropical mammals. 

 Amongst tropical eggs it is interesting to contrast the 

 deeply pigmented Nightingale-like eggs of Cossypha natal- 

 ensis, laid in tree-hollows in the dark places of dense forests, 

 with the cream or white eggs of ChalcojJelia afra and Colins 

 striatus that are laid not only in an open nest in isolated, 

 often semi-leafless, small trees or shrubs in grass-country at 

 the hottest time of the year, but are quite commonly exposed 

 to the direct sunlight. Prof. Newton gives a number of 

 similar instances [ibid. p. 189), and many will at once occur 

 to everyone. 



Wallace's view {' Darwinism,' 1889, pp. 122-126) 

 amounted to this : — All eggs were originally white. Those 

 species that have continued to protect their eggs from direct 

 observation — whether by laying in holes and domed nests, 

 by covering the eggs when they leave, or (themselves 

 possessing concealing coloration) by sitting close, or that, 

 being powerful or fighters, keep good guard over them — have 



I 



