90 VARIATION 



Variation in fertility. Certain birds regularly produce two 

 eggs, others three, and still others four, before incubation. The 

 average hen, following her natural habit, lays a " setting " 

 (ten to fourteen) and then suspends for incubation. The " crop " 

 of ova has been laid, and time is required for another to come 

 forward. The Maine station, however, has succeeded in greatly 

 increasing the production of eggs, and has produced one hen that 

 has laid two hundred and fifty-one eggs during a single year. 



Most cows produce only five or six calves, many only one or 

 two, and some not any, yet Old Granny (No. I in the Galloway 

 Herd Book) produced twenty-five, the last one in her twenty- 

 ninth year. The difference between regular and shy breeders 

 is the difference 'in the functional activity of the reproductive 

 organs, and next to performance ability it is the most impor- 

 tant character in the eyes of the breeder. Even longevity itself 

 is not its equal from the standpoint of the improver, because 

 quality cannot be said to exist in the race unless the individuals 

 that possess it are sufficiently fertile to insure its easy and 

 certain perpetuation. 



Accumulation of functional variations. Having shown the 

 marvelous differences in functional activity between different in- 

 dividuals, and having shown that these differences are hereditary, 

 as in corn, it follows necessarily that functional variations may be 

 accumulated into true breed distinctions, and that strains of 

 animals and plants may be permanently established with exceed- 

 ingly high efficiency in desired lines ; indeed, this has been already 

 accomplished, though we are still far short of what is possible. 



For example, the beef breeds are more economical producers 

 of meat than are the dairy breeds, and the converse is true as 

 to milk production. These two functions have, therefore, been 

 largely separated along breed lines. But it cannot be said that 

 one beef breed is more efficient than another in meat produc- 

 tion, or that any one dairy breed stands out preeminently as 

 the most economical producer of milk. This is partly because 

 breed differences have been largely built up along lines other 

 than those of efficiency, and partly because all breeds contain 

 many individuals of low efficiency in their own breed characters 

 and high efficiency in those of other breeds. Some Jerseys, 



