262 ON THE EGG. 



piper, and others, the course of the egg down the lower part of 

 the oviduct is spiral. 



The spots, streaks, and blotches are as a rule much more 

 commonly found at the big end of eggs — the part that offers the 

 greatest resistance to expulsion. Caps of black blood and rings 

 of the same are every now and then found, as on the eggs of the 

 titmouse, robin, and especially the razorbills, guillemots and gulls 

 and others, which are of varied ground colour and much spotted. 

 The sharp end is occasionally marked more than the big end. 

 Whichever end is very much more spotted or blotched than the 

 rest of the egg is that which passes first down the oviduct. The 

 big end being far the most marked end, passes therefore most 

 commonly first down, and it is first born or laid. Now there 

 seems every probability that the big end of an egg is the male 

 end, and we know that in the higher animals— the Mammalia, 

 it is the head which is the part first born. Sometimes under the 

 superficial layer of the shell bloodstains and blotches can easily 

 be detected. 



At one end of the egg, most commonly at the big end, there 

 is a cavity formed by a division, or separation of the two laminaj 

 of the shell membrane. One continues to the end of the egg, 

 lining the shell; the other crosses the interior, bounding the 

 white and separating it from the cavity. This is provided for 

 containing air, which is to serve for a short time the respiration 

 of the embryo before it is hatched. The air contained in it is 

 said to contain more oxygen than the air external to it. This 

 however has not been confirmed. 



An egg, then, coloured or not coloured, consists of shell, shell- 

 membrane, white, and yolk. The last is the principal or essential 

 part of the egg, the others only accessory, and which in the eggs 

 of some of the lower animals, as fishes, etc., are wanting. The 

 shell is composed almost altogether of carbonate of lime, mostly 

 smooth, and is porous, allowing of the passage of air. The shell 

 membrane adheres to both shell and white, and is beautifully 

 fibrous. The white is composed of concentric layers, which can 

 be shown by careful boiling when they become coagulated and 

 may be separated. It is entirely composed of albumen, which 



