APPLICATION OF PRINCIPLES. 109 



lastly again females, he explains by the theory, the first eggs 

 are not fully developed when laid and impregnated, that the 

 second lot laid later have had more time to undergo full devel- 

 opment, while the last laid arc but partially developed on ac- 

 count of the comparatively exhausted condition of the oviduct. 

 Under his instructions, George Cornaz, an intelligent agricul- 

 turist in Vaud, applied the principle to breeding cattle. He had 

 twenty-two Swiss cows served by a Durham bull on the first 

 signs of heat, and all brought forth heifers. He had six Swiss 

 cows served in the last stages of heat, by the same bull, with 

 the view of raising work oxen, and all produced bull-calves. 

 He had an imported Durham cow served, the last day of heat, 

 to obtain a pure successor to his valuable Durham bull, and his 

 wishes were crowned with success. This looks like solid ground, 

 but alas ! subsequent experiments made by Coste and others, on 

 cattle, rabbits, birds, frogs and fishes, have given uncertain and 

 contradictory results. It is difficult to set aside altogether the 

 results obtained by Cornaz, and, on the whole, there is probably 

 some truth at the foundation of the theory, but even if so, it 

 must be granted that modifying circumstances will often, if not 

 usually, set aside the rule. 



And lastly, the proposal to breed in and perpetuate the ten- 

 dency to produce young of one sex only, though exceedingly 

 plausible in what it offers, will probably prove still more worth- 

 less. I am not aware that the attempt has been made to per- 

 petuate such a power in the lower animals, but my own obser- 

 vations on human families are altogether unfavorable to its 

 success. One family of six daughters, all married and all pro- 

 lific, had each about an equal number of sons and daughters ; 

 and another family of seven daughters and one son, have so far 

 had families equally well balanced as regards the sexes. 



SUMMARY OF GENERAL PRINCIPLES. 



To recapitulate, we have seen : — 



1. That a perfect development and a sound and vigorous 

 health, constitutionally, and above all locally in the generative 

 organs, are conditions of fertility. 



2. That in the maintenance and improvement of a breed 

 the truth that like produces like, that the reproductive germ, 

 ovum or spermatozoon will stamp upon the animal developed 



