80 PKINCIPLES OF STOCK-BREEDING. 



termed, until it is represented mathematically by a 

 fraction so small as to scarcely merit attention, and 

 yet, as frequently observed, it may again appear in a 

 manner indicating that it has been constantly trans- 

 mitted, without change, through a long series of gen- 

 erations. 



Mr. Sedgwick remarks, in regard to atavism in 

 disease, that "no fixed boundaries, recognizable by 

 us, can be expected to limit its operation, for, like 

 other general laws in Nature, unity in principle coex- 

 ists with variety in results ; and it is chiefly because 

 we are less familiar with the results of atavism in dis- 

 ease than we are with many other reproductive phe- 

 nomena, as, for .the sake of illustration, with memory, 

 that we hesitate to accept them, although they are 

 not, in themselves, more exceptional or peculiar than 

 some of those are which we not only never hesitate to 

 accept, but with which this phenomenon in morbid 

 development seems to be closely allied. For atavism 

 in disease appears to be but an instance of memory in 

 reproduction, as imitation is expressed in direct de- 

 scent ; and in the same way that memory never, as it 

 were, dies out, but in some state always exists, so the 

 previous existence of some peculiarity in organization 

 may likewise be regarded as never absolutely lost in 

 succeeding generations, except by extinction of race." ' 



It has been remarked that no two animals are pre- 

 cisely alike, in all details of the organization, no mat- 

 ter how close the relationship or how striking the re- 

 semblance ; and, in connection with this, it has been 

 observed that instances occur in which individuals 



1 British and Foreign Medico- CMrurgical Review^ July, 1863, p. 197. 



