Egg in Birds, and the nature and seat of the Colour. 1 73 



liowcver evidently present in those of Ardea Herodias, Fidigula 

 mollissima, Sterna arctica, &e. In some instances the most super- 

 .iicial layer which I have been able to detect possesses no distinct 

 cellular structure properly so called, but might be described as 

 mostly granular, as in the wheat-ear, kestrel, mocking-bird, &c., 

 or granulo-cellular, as in the egg of the darter from S. Carolina. 

 In the epithelium of the ^^^ of the wheat-ear, the granules when 

 highly magnified seem to be often in linear and branched series, 

 presenting therefore a faintly fibrous appearance. 



Basement Membrane. — This layer, which is very evident in 

 some instances, is not so easily observed in others. It is usually 

 of very delicate structure, rendering careful manipulation neces- 

 sary to demonstrate its presence. It is well-developed in the egg 

 of the ostrich, in which its structure is densely granular. In the 

 e^^ of the lapwing, &c., the granules under a high power appear 

 to have a linear and sometimes branched arrangement, thus ap- 

 parently presenting a transition to the fibrous structure. 



In eggs of considerable size with a strong shell there appear 

 to be several layers, at least of epithelium if not also of basement 

 membrane, and in several instances the structural difference be- 

 tween the two is not very evident, there being a passage of one 

 into the other. 



In some cases, as in the g^^ of the blackbird, &c., there may 

 be observed, first a delicate epithelium, beneath it a basement 

 membrane, and lastly a single layer of loose fibrous tissue. 



The colours of eggs may be viewed under two heads, first the 

 ground colour, second the spots or blotches ; these last are of 

 various forms and sizes, and may either have a well-defined di- 

 stinct outline, or their outline may be ill -defined. 



M. Des Murs, in his remarks on this subject, inquires whether 

 these colours are due to the chemical combination of sanguineous 

 matter with the calcareous shell, or whether they are specially 

 secreted by peculiar glands. He states that the minute papillae 

 which line the oviduct, and which pour into it the calcareous 

 matter to form the shell, do also give vent at the time of egg- 

 laying to sanguineous exudations which may cause the colour. 

 But on the other hand he relates that he once found a lapwing's 

 e^^ of a uniform green, almost wholly spotless. On blowing 

 out the yolk and albumen, he further expelled a black and glairy 

 lump, consisting of an agglomeration of the colouring matter, of 

 a greenish brown, floating in albumen, and inclosed in a trans- 

 parent follicle. This he says would seem to show that the colour- 

 ing matter is a special secretion prepared beforehand in the 

 oviduct, and in the present case he supposes that the mass of 

 colouring matter had by some accident become inclosed within 

 the shell instead of being distributed over its outer surface. 



