Artificial Incnhation. 197 



The natural Incubation of chickens and other domestic 

 fowl;!, and of partridges and pheasants, continues ordinarily 

 twenty-one days. Ducks, geese, and turkeys, require thirty- 

 six. The artificial process in Mr. Barlow's oven is of the 

 same duration, and it would be injurious to accelerate or 

 retard it. As soon as the chicks have broken their shells, 

 they are placed in a cage beneath the oven, the temperature 

 of which is at eighty degrees Fahrenheit. Here they are left 

 three or four days, during which the temperature is gradually 

 diminished. They are then exposed to the open air, and in 

 general they are as robust as those that are hatched under 

 hens. 



Mr. Barlow states the progressive developement of the 

 germ, fiom actual examination, to be as follows : 



The egg has been exposed to the oven scarcely twelve 

 hours, when the form of the embryo is distinctly perceived. 

 The second day, the heart begins to beat; on the third, 

 appear two vesicles full of blood, the pulsations of which are 

 very sensible : the one. is the left ventricle, the other the 

 base of the great arter3\ On the fourth, the wings are dis- 

 tinguished, and on the head two protuberances for the brain, 

 one' for the bill, and two for the anterior and posterior parts 

 of the head. The fifth witnesses the developement of the 

 auricles of the heart. About the sixth the liver is distin- 

 guished. The first voluntary movement of the embryo is 

 manifest at the end of the I3lst hour. At the 138th are 

 seen the lungs and the stomach, and on the seventh day, 

 the mtestines, the kidneys, the upper jaw, and two drops of 

 blood in place of the one before observed ; the brain acquires 

 some consistence. On the 8th day the bill opens, and the 

 breast is covered with flesh ; on the Oth the ribs issue from 

 the spine, and the gall bladder is perceived; on the 10th 

 the bill becomes green, and if the animal is disengaged of its 

 integuments it can move itself sensibly. On the 1 1th (he 

 feathers begin to shoot, and the skull to be solidified. On 

 the 1 2th the eyes appear, and the ribs acquire their devel- 

 opement. On the 13th the spleen approaches the stomach, 

 and on the 14th and 15th it augments in volume. On the 

 16th the bill opens and shuts, and about the 18th the ihick 

 utters the first cry. From this time the animal gradually 

 increases in strength until it breaks the shell. 



