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XXV. Observations on the changes the egg lindergoes during 
incubation in the common fowl , illustrated by microscopical 
drawings. By Sir Everard Home, Bart. V. P. R. S. 
Read May 1 6, 1822. 
This has been a favourite subject with many of the most 
celebrated anatomists. The great Harvey, Malpighi, and 
John Hunter, have done more than any others in the ad- 
vancement of this enquiry. 
Hunter's observations were never rendered so complete 
as to induce him to publish them ; but what he has done is 
open to the public, both in the preparations in his Collection, 
and in his Cabinet of Drawings. 
In these last, the vesicle which begins near the rectum, and 
afterwards envelopes the embryo, is clearly made out. 
In the year 1815, Mr. Dutrochet, an ingenious French 
anatomist, laid a Memoire upon this subject before the French 
Academie. Mr. G. Cuvier has given a Report upon this 
Memoire, but has not given the Memoire itself. He con- 
siders the author to be the first person who has clearly ex- 
plained the rise and progress of the vesicle ; but some of Mr. 
Hunter's drawings of it are dated 1773, the year I went to 
live in his house. 
After all that has been done, much is still wanting to render 
the investigation complete ; and to promote this object, the 
following Observations and Drawings are brought before the 
Society. 
The gelatinous molecule, from which the future embryo 
