E(jg in Birds, and the natwe and seat of the Colour. 175 



usually blue witli generally well-defined black spots ; the epithe- 

 lium is veiy thin ; the black spots mostly reside in it, and are 

 produced by the congregation of minute pigment-granules which 

 are of a dark brown ; the ground colour is seated in the layer 

 beneath. 



In the egg of the kittiwake the epithelium is thin and almost 

 colourless y the well-defined spots are seated in it. The deeper 

 layer is of greater density, and is the principal seat of the ground 

 colour and of those spots which have an indistinct outhne. A 

 similar arrangement occurs in the egg of Larus glaucus. In 

 some cases the pigment-granules do not appear to be contained 

 in cells, but merely densely congregated ; in other cases, ihQSteima 

 Hirundoj Linn., for example, the pigment-cells are quite evident. 

 If after removing the calcareous matter by means of an acid, 

 the remaining coloured membranes of the egg of Turdus muste- 

 linuSj hedge-sparrow, &c., be macerated in alcohol, a blue solu- 

 tion will be obtained, which, when allowed to evaporate on white 

 paper, leaves a permanent blue stain. 



My friend Mr. Peter Grant has contributed the following notes 

 respecting the action of certain agents upon the membranes 

 (bluish green) of the egg of the foolish guillemot, after the cal- 

 careous matter has been removed. They are not changed by cold 

 concentrated nitric acid, but are bleached by chlorine ; strong 

 fuming nitrous acid changes the colour to orange-brown ; the 

 addition of water changes that colour to grayish yellow. Iodine 

 colours the membrane a deep orange-brown ; on adding potash 

 this colour is destroyed ; the potash being removed by washing 

 and iodine added, the same colour is produced as before ; potash 

 again decolorises it, and so on repeatedly. The membranes by 

 long digestion in concentrated solution of potash gave a yellow 

 solution, which with acetic acid in excess gave copious white 

 flocks. The supernatant liquor afforded distinct indications of 

 the presence of copper. The white flocks when washed and 

 treated with iodine became gray, but were decolorised by potash. 

 Concentrated nitrous acid was coloured yellowish by standing 

 over them ; the addition of water gave grayish flocks ; the super- 

 natant liquor with carbonate of ammonia yielded more flocks of 

 a gray-yellow, which dissolved in dilute sulphuric acid; the am- 

 moniacal liquid gave slight traces of copper. 



The shell first deprived of epithelium and then boiled dui'ing 

 two hours in concentrated solution of potass gave a dark yellow 

 solution leaving a purple-olive sediment. This solution afforded 

 evident indications of the presence of copper and manganese. 



The olive sediment after being washed was found to be inso- 

 luble in muriatic or even strong nitro-muriatic acid. Boiled in 

 nitric acid it gave a deep yellow solution, leaving a slight residue 



