THE EGG 



95 



either because the bird has not eaten enough of shell forming 

 feed, or because there is disease of the oviduct. The grow- 

 ing chick must breathe while in the shell, and nature has 

 provided for this by making the shell porous, with hundreds 

 and hundreds of small openings, through which the air passes, 

 and through these same openings the liquid part of the egg 

 evaporates. Shells vary greatly in color and structure. The 

 Leghorn lays a white egg, which is rather brittle and thin, 

 and the heavier breeds usually lay dark or brown eggs, which 

 are much thicker and tougher. Owing to an abnormal 

 condition of the oviduct, eggs are sometimes laid with irregu- 



Germ (found only 

 infertile e^^s) 



■Shell 



''utershell memhTune 

 ^nnershell memhmne 



Cha.2a.za 



^Thinalbvmen 

 '^Medium acumen 

 ^ea.yy or thick 

 Btlbumen. 



Fig. 59. — The cross-section of an egg showing the location of the contents. 



lar shells; often they are spotted and rough. In collecting 

 eggs for hatching, only the clean, smooth-shelled ones should 

 be used. The liquid part of the egg evaporates very quickly 

 in a warm temperature, and the best way in which to check 

 it is to lower the temperature or, if possible, to close the 

 pores in the shell. Commercial cold storage means the 

 keeping of eggs at a low temperature to prevent evaporation. 

 In the home eggs are often preserved by placing them in a 

 solution of silicate of soda, which coats the egg, and thus 

 closes the pores or openings in the shell (Fig. 59). 



There are two shell membranes lying immediately imder 

 the shell, and in close contact with it. These are called the 

 outer and inner membranes. The outer one lines the shell 



