38 PRINCIPLES OF STOCK-BREEDING. 



"First year after birth . . . . 15 to 20 



Second u " " . . . . 100 " 120 



Third " " " .... 120 " 135 



Fourth " " " . . . . 100 " 115 



Fifth " " " .... 60 " 80 



Sixth """.... 50 " 60 



Seventh " " " .... 35 " 40 



Eighth """.... 15 " 20 



Ninth .... 1 " 10 '" 



Dr. Duncan, in summing up the results of an ex- 

 tended collection of statistics relating to births, shows 

 that a similar law prevails among women. While 

 those under twenty years of age are less fecund than 

 those between twenty and twenty-four, a gradual in- 

 crease in productiveness is made to the age of thirty 

 years, which is the most prolific age, after which a 

 rapid decrease in fertility takes place. 9 



The influence of diminished fecundity in young 

 mothers upon their offspring, that necessarily inherit 

 the same peculiarity, would tend to predispose to bar- 

 renness and sterility in the breed or family in which 

 early breeding is frequently practised ; while the de- 

 fective development of the mother, arising from the 

 same cause, would become a constitutional peculiarity 

 in the offspring. 



As the retarded development of the mother and 

 the defective condition of the germ or egg are both 

 the result of immaturity, and a consequent deficiency 

 in constitutional vigor, which, as we have seen, will 

 undoubtedly be transmitted, they must have a marked 



1 " Poultry-Breeding," p. 27. 



a Dr. Duncan, " Fecundity, Fertility, and Sterility," as quoted in 

 Walford's " Insurance Cyclopaedia," vol. Hi., p. 194. 



