SOME SUGGESTIONS FOR BIRD STUDY. 



95 



interference from without, but chiefly serve to maintain 

 heat within and to regulate evaporation. 



The colourless almost fluid substance which coagulates 

 to a white solid on boiling consists of albumen, a substance 

 containing six chemical elements, Carbon, Oxygen, Hydro- 

 gen, Nitrogen, Phosphorus, Sulphur. It is in three layers, 

 which may be observed flaking apart on cutting a hard 

 boiled egg. Within the albumen we are familiar with the 

 yolk enclosed by a delicate membrane from which there 

 passes towards each end of the egg a thickened twisted 

 cord of albumen. The cords or chalazae which end in the 



Fig. 24. Diagram to show the parts of a fowl's egg as seen in longitudinal 

 section. The parts represented are the shell and its membranes, air 

 space, albumen in which may be seen the thickened cords (chalazae), 

 yolk in layers with the position of the germ indicated by the dark 

 patch at the top. 



middle layer of albumen, suspend the yolk ; they prevent it 

 spinning rapidly when the egg is rolled or turned quickly, 

 and they act as buffers to the yolk in the event of its 

 receiving sudden jolts. 



The yolk, golden yellow in colour, wjhich consists of 

 several organic substances, serves to nourish the developing 

 bird within the egg. It is not of uniform composition, 

 the inner contents being lighter. Just above where this 

 lighter mass comes to the surface of the yolk, there lies 

 the germ. Owing to this arrangement, no matter how 

 the egg lies, the yolk rotates on the chalazae so that the 



