12 THE HEN'S EGG. [CHAP. 



2. Lining the shell, is the shell-membrane, which is 

 double, being made up of two layers; an outer thicker 

 (Fig. 1, s. m.), and an inner thinner one (i. s. m.). Both of 

 these layers consist of several laminae of felted fibres of l 

 various sizes, intermediate in nature between connective 

 and elastic fibres. 



FIG. i. 



ch.l. 



DIAGRAMMATIC SECTION OF AN UNTNCUBATED FOWL'S EGG 

 (modified from Allen Thomson). 



bl. blastoderm, w. y. white yolk. This consists of a central flask-shaped 

 mass and a number of layers concentrically arranged around this. 

 y. y. yellow yolk. v. t. vitelline membrane, x. layer of more fluid 

 albumen immediately surrounding the yolk. w. albumen consisting of 

 alternate denser and more fluid layers, ch. I. chalaza. a. ch. air-chamber 

 at the broad end of the egg. This chamber is merely a space left between 

 the two layers of the shell-membrane, i. s. m. internal layer of shell- 

 membrane, s. m. external layer of shell-membrane, s. shell. 



Over the greater part of the egg the two layers of the 

 shell-membrane remain permanently in close apposition 

 to each other; but at the broad end they tend to separate, 

 and thus to develope between them a space into which air 

 finds its way. This air-chamber, as it is called, is not to be 

 found in perfectly fresh eggs, but makes its appearance in 



