GENERATION AND DEVELOPMENT. 



blood-vessels extend, and in which they are, with the 

 gradually developed. The gall-bladder is developed as a 

 diverticulum from the hepatic duct. 



Fig. 242.* 



Development of the Respiratory Apparatus. 

 The lungs, at their first - development, appear as small 

 tubercles, or diverticula from the abdominal surface of the 



Elff. 243.f 

 A. B C 



* Fig. 242. Rudiments of the liver on the iutestiue of a chick at the 

 fifth day of incubation, i, heart ; 2, intestine ; 3, diverticulum of the 

 intestine on which the liver (4) is developed ; 5, part of the mucous 

 layer of the germinal membrane. 



t Fig. 243, illustrates the development of the respiratory organs. A, 

 is the oesophagus of a chick on the fourth day of incubation, with the 

 rudiments of the trachea on the lung of the left side, viewed laterally : 

 i, the inferior wall of the oesophagus ; 2, the upper wall of the same 

 tube ; 3, the rudimentary lung ; 4, the stomach. B, is the same object 

 seen from below, so that both lungs are visible, c, shows the tongue and 

 respiratory organs of the embryo of a horse : i, the tongue ; 2, the larynx : 

 3, the trachea ; 4, the lungs viewed from the upper side. After Rathke. 



