ss. 
“Sy 
of the Sexes in Plants, Animals, and Man. ~ 71 
furnish males. But if it happens that a second generative period 
succeeds the first one, or if the external or organic conditions 
change considerably, the last ova may not attain to the superior 
degree of maturation, and may again furnish females. 
Ceteris paribus, the application of the principle of sexuality is 
less easy in the case of multiparous animals. 
5. In the application of the above principles to the larger 
Mammalia, it is necessary that the experimenter should first of 
all observe the course of the phenomena of heat in the very in- 
dividual upon which he proposes to act, in order that he may 
know exactly the duration and the signs of the rutting-season, 
which frequently vary in different individuals. 
6. It is evident that no certain result can be expected when 
the signs of heat are vague or equivocal. This is scarcely ever 
the case in animals living in a state of freedom ; but cattle in 
the fattening-sheds or in the stable sometimes present this ab- 
normal peculiarity. Such animals must be excluded from ex- 
perimentation. 
7. From the mode in which the law ruling the production of 
the sexes has been deduced, it results that this law must be 
general and apply to all organized beings,—that is to say, to 
plants, animals, and man. 
It is necessary to distinguish carefully the law itself (1 and 2 
of this summary), which is absolute, from the applications of it 
which may be made with more or less facility. 
Third Part. Notice by M. George Cornaz. 
I, the undersigned, George Cornaz, administrator of the estate 
of my father, the late M. A. Cornaz, President of the Agricultural 
Society of “ La Suisse Romande,” at Montet, in the Canton de 
Vaud, certify that I received from M. Thury, Professor in the 
Academy of Geneva, under date of the 18th February 1861, 
some confidential instructions the object of which was an experi- 
mental verification of the law which governs the production of 
sex in animals. 
I have applied to the management of my herd of cows the 
data furnished to me by M. Thury, and obtained at once, with- 
out any uncertainty, all the expected results. 
In the first place, in twenty-two successive cases, I wished to 
obtain heifers ; my cows were of the Schwitz breed, and my bull 
a pure Durham; the heifers were in demand amongst breeders, 
and the bulls were only sold to the butchers. I obtained the 
desired result in all cases. 
Having subsequently purchased a cow of pure Durham breed, 
I desired to obtain from them a new bull, which might replace 
the one which I had bought at great cost, without waiting for 
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