1922.] ^^//"^ ^/"Fratorcnla arctica. 257 



with nearly all other eggs, loill he found to he the same colour 

 as the superficial pigment. The thin lime layer which covers 

 the underlying pigment is entirely responsible for the various 

 shades of grey and mauve which are partly visible to the 

 unaided eye, and which are usually called shell or under- 

 lying markings. 



I found, however, that the scraping away of the lime was 

 not altogether satisfactory or sufficient to expose the \vholo 

 of the hidden pigment, or to give an accurate idea as to the 

 density and abundance of the pigment; pigment was found 

 overlying pigment with the thinnest possible limo layer in 

 between. There was also the danger of the whole structure 

 collapsing, it being necessary in some instances to remove 

 the lime almost to the membrane. 



If the egg is held to a strong artificial light, and it is 

 examined througli the blowhole, much of this pigment can 

 be seen ; even this method is insufficient, and only partly 

 reveals the great beauty of the eggs as a whole. 



Both of the foregoing experiments, I believe, are known 

 to many oologists, and are perhaps sufficient for some 

 purposes ; they do not, however, as already pointed out, 

 convey the slightest idea as to how heavily pigmented these 

 eggs really are. 



The following original experiment — of which I gave a 

 demonstration at the last oological Dinner on 14 September, 

 1921, and again at the October meeting of the B.O.C/. — 

 gives the most remarkable results, as the photojiraphs 

 (Plate II.) appended to this article testify. The upper six 

 eggs (figs. 1-6) on the ])late are unillnminated, the lower six 

 (figs. 1 a— 6 a) are the same eggs illuminated with electricity 

 from inside the e^igs ; from the lower figures it will be seen 

 that the eggs are as well marked as some of the most heavily 

 pigmented eggs of Alca torda, to which it wdll be seen, when 

 illuminated, they have some affinity in regard to the form and 

 arrangement of the markings. They were illuminated from 

 six dry batteries with half-inch bulbs inside each egg. 



Puffins' eggs are obviously in a very rudimentary stage. 

 What useful purpose do these concealed markings serve ? 

 They cannot in any way help to protect or conceal the eggs. 



SER. XI. — VOL. IV. s 



