Colour Variation in Eggs. 581 



better known as Oochlorin ; while no traces of Lichnoxan- 

 thine have been found by subsequent observers in any shell, 

 and probably Sorby's results were due to the presence of 

 minute fungi or mould upon the shells. 



Oorhodein appears to be present in greater or smaller 

 quantities in almost all coloured eggs which show traces of 

 red, brown, black or grey markings, or are of any shade of 

 pink, olive or brown, sometimes alone, and frequently to- 

 gether with traces of Oochlorin and Bili verdin. (The Crypturi 

 appear to form an exception to this rule, and here the red 

 appears to be due to Ooxanthin preponderating largely over 

 Biliverdin.) To Biliverdin in a pure state may be ascribed 

 the blue tint which forms the ground colour of certain eggs, 

 while in combination with Oochlorin it forms green, and 

 various shades of olive in conjunction with Oorhodein. 



Having thus indicated the main constituents of colour in 

 eggs we will now proceed to consider the principal variations 

 which are to be found, more especially among birds whose 

 eggs are normally more or less coloured. 



It will be found that the chief variations from the normal 

 type fall naturally into three main classes : Firstly, those in 

 which there is either a deficiency or a total absence of the one 

 or more pigments normally present ; secondly, those. in which a 

 pigment is present, which is normally absent ; and thirdly, 

 those in which at least two pigments are normally present in 

 varying proportions, and sometimes one and sometimes the 

 other predominates. 



(1) Under the first head we may place those cases in which 

 eggs normally coloured by Biliverdin are found devoid 

 of colouring matter. Thus pure white eggs of Sturnus 

 vulgaris are occasionally met with. At other times eggs 

 which are coloured chiefly, if not entirely, by Oorhodein, 

 are found colourless, e.g., Lagopus scoticus, Gerchneis 

 iinnunculus, Erithacus rubecula, etc. A third case is that 

 in which at least two pigments are normally present 

 (such as Linola cannabina, Ligurinus cliloris, Pyrrhula 

 europœa, etc.), but eggs without markings or ground 

 colour are sometimes found. To give a complete list of 

 those species in which this variation occurs would take 



