igiS.] Erythrism in Birds' Eygs. 69 



have been attempted beyond the exhibition of many most 

 beautiful and extraordinary eggs. 



In view, therefore, of the fact that the subject is so novel 

 a one, my remarks must be held as purely suggestive of the 

 lines upon which we might work in trying to ascertain what 

 erythrism can teach us. It must also be remembered that 

 erythrism, or its absence, is only one of many characters of 

 each egg, and its value can only be estimated when con- 

 sidered in combination with the others. 



Probably the first point which would strike any one on 

 examining a really large collection of eggs is the extra- 

 ordinary and erratic distribution of erythrism. In some 

 cases it appears to be both constant and consistent through- 

 out a whole order, family, genus, or species, whilst in others 

 there appears to be no limit to its variation. The second 

 point which would strike the systematist is that, as with 

 birds themselves so with their eggs, a character of the 

 greatest help in one family, genus or species is of no use 

 whatever in another. But even with these two points con- 

 ceded, it still appears to me that erythrism may be justly 

 used as an aid in determining, or as a guide to the deter- 

 mination of, bird classification. 



In the following remarks I propose to very briefly outline 

 facts already ascertained, and a possible way in which these 

 facts may be developed scientifically and some deductions 

 drawn from them. 



The simplest way will probably be to consider orders, 

 families, genera, species and subspecies in the sequence as 

 written, and to deal with normal erythrism first. 



As regards orders, we find that there are some which nor- 

 mally contain no erythristic eggs, others which contain both 

 erythristic and non-erythristic eggs, a few in which erythrism 

 is the dominant colour, and still fewer in which all the indi- 

 viduals lay erythristic eggs. It is not easy, however, to think 

 oi any order in which there are not few or many exceptions 

 to the general rule of erythrism, but, taken as a whole, the 

 eggs of the Accipitres must be considered as forming a good 



