70 Prof. Thury on the Law of the Production 



It is plain that, according to the author, the life of the un- 

 fecundated ovum is divisible into two periods. In the first of 

 these it is in principle a female ovum, in the second a male 

 ovum. The turning moment {moment de vire), according to the 

 author, is the time (probably very short) which separates the 

 two periods, and in which the natural course of development 

 induces some sudden change, the nature of which histology 

 should reveal to us. He assumes that the relative duration of 

 the two periods of the life of the ovum may be modified under 

 the influence of the organic state of the female, whence would 

 result a predisposition on the part of some females to give birth 

 either to individuals of their own sex or to males. Temperature, 

 by its direct action upon the ovum, and the influence of the 

 fecundating male upon the organic condition of the female, 

 would also produce similar results. 



The author, in all his deductions, appears to start from a 

 general point of view, which he certainly indicates, but nowhere 

 demonstrates in a positive manner, regarding it apparently as a 

 sort of axiom. He assumes that " sexual life, being common to 

 animals and plants, must be subjected to identical fundamental laws 

 in both kingdoms." If this be true of the two kingdoms, it must 

 apply with still more reason to the various divisions of the same 

 kingdom. This admits of much generalization ; but (and this is 

 the difficulty) we have yet to distinguish with certainty the facts 

 which bear upon essential laws from the infinitely varied mani- 

 festations by which these same laws are realized in combination. 



The second and third parts of M. Thury's memoir are here 

 reproduced entire. 



Second Part. Summary and Practical Observations. 



1. Sex depends on the degree of maturation of the ovum at 

 the moment of its fecundation. 



2. The ovum which has not attained a certain degree of ma- 

 turation, if it be fecundated, produces a female ; when this de- 

 gree of maturation is passed, the ovum, if fecundated, produces 

 a male. 



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

 the ovary to descend slowly through the genital canal (as in uni- 

 parous animals), it is sufiicient that the fecundation takes place 

 at the commencement 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 

 during a single generative period (multiparous animals and ovi- 

 parous animals in general), the first ova are generally the least 

 developed, and produce females ; the last are more mature, and 



