44 
MEMOIR OF 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 sendee 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 obsen'ed during incubation. After 
the egg has been subjected to the process of incuba- 
tion for 
7 hours, the membrane of the yolk appears. 
1 2 do. the peculiar envelope (the amnios) of the chick appeal's. 
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 tliree cavities of the heart. 
72 do. end of three days, the wings and legs appear. 
96 do. four do. tho 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-one do. chick liberated from the shell. 
