VARIATION. 103 



much ease as the fleetest of their race in this conn- 



try.'" 



In the modifications of form, habits, instincts, and 

 general activity of the functions of organs, resulting 

 from the agencies under consideration, the principle 

 of correlation, to which we have already referred, may 

 be readily traced. 



We cannot, in fact, make a decided change in any 

 part of the system without producing a corresponding 

 modification of some other part that is correlated 

 with it. 



The tendency to early maturity, which is so highly 

 developed in the meat-producing breeds, is accom- 

 panied with a change in the period of dentition, and 

 this fact has to be taken into account in determining 

 the age of animals by the teeth. 3 



There is not only a difficulty in producing a con- 

 siderable modification of several characters at the same 

 time, but there is also the danger of suppressing some 

 character we wish to retain, by the development of a 

 new one not in harmony with it. 



Family characteristics are produced by limiting 

 the range of variations to the particular standard the 

 breeder wishes to establish. The greatest skill will 

 be required in establishing the family type, to retain,, 

 in connection with the desired characters, the qual- 

 ities that give vigor to the constitution and insure 

 an active performance of the function of reproduc- 

 tion, and to prevent, at the same time, the develop- 



1 Quoted from " Cyclopaedia of Anatomy and Physiology," vol. iv., 

 p. 1303. 



2 Journal of the Royal Agricultural Society, vol. xv., p. 323. 



