EXPLANATION OF THE PLATES. 



Fig. 8. The embryo six days old with the allantois separated 

 from the area vasculosa and the yolk, &c. 



Fig. 9. The embryo of the ninth day of development, seen 

 through the allantois, which now invests nearly 

 the entire surface of the yolk, and beneath which 

 the collapsed and faintly coloured vessels of the 

 area vasculosa may still be discerned. The purpose 

 fulfilled by the distribution of such innumerable 

 vessels in the membrane of the area vasculosa, and, 

 subsequently in the allantois, is but temporary, and 

 is doubtless connected with respiration, the blood 

 in these vessels being submitted to the influence 

 of the oxygen of the air which enters the egg 

 through the pores contained in its shell ; the vital 

 fluid is thus regenerated and afterwards reconveyed 

 to the embryo itself, from which it first proceeded. 

 At the completion of the development of the chick, 

 the allantois undergoes the same obliteration of its 

 vessels which the area vasculosa previously suffered. 



Fig. 10. The embryo at the end of the seventh day of 

 development removed from its membranes. 



Fig. 11. The same at the end of the ninth day, also separated 



from its membranes. 

 Such is a brief sketch of the marvellous development of 



the embryo of the chick. 



