ZOOLOGY. 325 



1 . Sex, according to Prof. Tlmry, depends on the degree of matu- 

 ration of the ovum at the moment of its fecundation, 



2. Tin 1 ovum which has not attained a certain degree of maturation, 

 if it be fecundated, produces a female ; when this degree of maturation 

 is passed, the ovum, if fecundated, produces a male. 



o. When, at the rutting-season, a single ovum separates from the 

 ovary to descend slowly through the genital canal (as in nniparous 

 animals), it is sufficient that the fecundation takes place at the com- 

 mencement of the rutting-season to produce females, and at the end 

 to produce males, the turning point of the ovum occurring normally 

 during its passage in the genital canal. 



4. When several ova separate successively from the ovary dur- 

 ing a single generative period (multiparous and oviparous animals in 

 general), the iirst ova are generally the least developed, and produce 

 females; the last are more mature, and furnish males. But if it hap- 

 pens 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. Cceteris 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 Mamma- 

 lia, it is necessary that the experimenter should first of all observe the 

 course of the phenomena of heat in the very individual 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 diii'erent in- 

 dividuals. 



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 abnormal peculiarity. Such 

 animals must be excluded from experimentation. 



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. 



In the Annual of Scientific Discovery for 1864, p. 292, some state- 

 ments were given of the experience of M. Cornaz, a Swiss agricultur- 

 ist, in applying M. Thury's theory in cattle breeding. M. Nickles, the 

 Paris correspondent of SHU mail's Journal also furnishes some informa- 

 tion bearing upon the subject. lie says : "According to M. Thury, 

 the product is always of the male sex when the fertilization of the ovq, 

 occurs at complete maturity, and is always female when it takes place 

 at a less advanced period. 



There is a very simple way of solving this problem. It is to select 

 for experiment species that come to maturity in succession, and, that 

 during a single impregnation, fertilize the whole series of ova which 

 detach themselves from the ovary during a period of 8, 10, 12, 15, 

 or even. 18 days. We know, indeed, that, in case of the hen, a 

 single couplin^ suffices for the fertilization of five, six, or even seven 



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