< MEMOIR OP BARON HALLER. 



osity, and which his extraordinary industry and 

 ingenuity turned to account. It was under these 

 circumstances that he began to direct a peculiar 

 attention to the structure of the egg and the growth 

 of the chick, and for three years bestowed upon this 

 subject the most minute investigation which it has 

 probably ever received. He made almost innumer- 

 able microscopic observations, and in a distinct work 

 gave a detailed account of two hundred and eighty 

 four of them. This treatise was subsequently in- 

 corporated into his great work on physiology, and 

 as the subject in question is at once so interesting and 

 important, we shall only be rendering a most accept- 

 able service to our readers, by presenting them even 

 with a very abridged account of his conclusions. 



Before, however, doing so, we shall give, in a 

 tabular form, the dates of the most striking pheno- 

 mena which are observed during incubation. After 

 the egg has been subjected to the process of incuba- 

 tion for 



7 hours, the membrane of the yolk appears. 



12 do. the peculiar envelope (the anrnios) of the chick appears. 



24 do. the envelope is perfect. 



31 do. the venous figure appears. 



45 do. this venous figure is completed. 



48 do. the heart appears, and begins to pulsate. 



55 do. first appearance of three cavities of the heart. 



72 do. end of three days, the wings and legs appear. 



96 do. four do. the two ventricles of the heart are seen ; 



liver appears. 



120 do. five do. ventricles of the heart completed. 

 144 do. six do. the bones appear. 

 240 do. ten do. first appearance of the feathers. 

 451 do. eighteen do. first cries of the chick. 

 28 do. twenty-ooe do. chick liberated from the shell 



