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. 



Cateris 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 difierent 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 Roraande," 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 



