M. Saint-Hilaire on the Females of' Pheasants, cj-c 9 



yet the difference is so marked as to leave no doubt of the 

 main fact, that a very different result is obtained when* the 

 bodies are in motion, notwithstanding their equal powers when 

 at rest, which is, indeed, all I engaged to ascertain. I have 

 not at present had the pleasure of seeing M. Poisson's nume- 

 rical deductions, nor any sketch of his theory beyond what 

 was contained in your last number ; it will therefore be very 

 gratifying to me if it should be found, when the theory and 

 experiments are compared, that the agreement is as close as 

 from the nature of the operation we have any just reason to 

 expect. 



Royal Military Academy, 

 28d October 1826. 



Art. III. — On the Females of Pheasants which assume the 

 plumage of the male. By M. Isidore Geoffroy Saint- 

 Hilaire. * 



The name of Faisans Coquards is applied by sportsmen to 

 those pheasants whose plumage is tarnished and discoloured, 

 but in its colours resembles that of the male. It was long be- 

 lieved, and an inspection of their colours naturally led to the 

 idea, that these Jhisans coquards were males suffering under 

 sickness or in a bad state of plumage ; on the contrary, it is 

 now nearly half a century since we have been aware of the 

 facts that these birds are females ; a circumstance partly de- 

 tected by those who have reared them in a tame state, and 

 observed their developement, and partly by anatomical dis- 

 sections. The true sex of these pretended males was ascer- 

 tained both by Vicq-d'Azyr and Mauduit. 



Mauduit, the author of the ornithological department of 

 the Encyclopedic Methodique, is hitherto the only writer who 

 has furnished us with information on this interesting fact.— ■ 

 (See Article Orniihologie of that work, t. ii. p. 3.) 



u One fact in their history," says this philosopher, " known 

 to sportsmen, but I believe not mentioned by naturalists, is 

 too important to be omitted. Aged females, who have pro- 



l Translated from the Annates des Sciences Naturelles. 



