THE SELECTION- OF ANIMALS 41 



Some breeds of dairy cattle produce milk with a high 

 percentage of fat as a breed characteristic in the milk, 

 but only moderate in quantity. Such for instance are 

 the Jersey and Guernsey. They produce a quality in 

 milk which it has taken centuries of careful breeding to 

 reach; other breeds as the Holstein, produce a large flow 

 of milk with a relatively low per cent of butter fat, but 

 the claim that it is richer in casein may possibly be 

 correct. So fixed is the character of the transmission in 

 the instances cited, that years and years of careful breed- 

 ing and selection would be required to make any impor- 

 tant modification, for the reason that modification in 

 quality of production is far more difficult to attain than 

 modification in form. 



Contrasts in sheep, The wide and striking contrasts in 

 the character of the wool in sheep furnish notable in- 

 stances of the potency of transmission relating to quality 

 in production. In some breeds of sheep not more than 

 500 wool fibers are produced on one inch square of the 

 body, while on others as many as 1,500 have been pro- 

 duced. In some breeds the normal length of fibre is not 

 more than 2 to 3 inches, in others it is not less than 10 to 

 12 inches in very good specimens. To transform the one 

 kind of wool into the exact counterpart of the other, more 

 especially when the change is from extremely fine to ex- 

 tremely coarse or the opposite, would take more years 

 than are usually allotted to an average life. Some breeds 

 of sheep, as the Dorset, are very prolific, and the same is 

 true of some of the breeds of bacon swine; other breeds 

 in both classes produce less numerously and less regu- 

 larly. The breeding habit also influences the season for 

 breeding, as shown in the production of autumn lambs 

 by the Dorsets as a normal feature of production. But 

 modification in breeding habit is much more easily se- 

 cured than modification in quality of production. 



