106 THE DOMESTIC SHEEP. 



breeding sheep, and their acuteness in this way doubtless 

 advanced the value of the flocks very largely. 



Breeding is the art of influencing the character of any 

 animal by changing the conditions of -life, and regulating th'e 

 reproduction by selection of individuals, as well as by inten- 

 sifying by the best methods of feeding all the natural pro- 

 clivities. Thus there must be an adequate foundation to 

 begin with; a basis to stand upon; and in selecting this 

 starting point the natural or acquired ability of the breeder 

 plays a most important part. Thus we may say that there 

 are three general principles or laws by which the art of 

 breeding is made practical. These are heredity, selection 

 and variability. 



Heredity is a special function of all animals, and the 

 common maxim of the breeder, that, "like produces like," 

 is to be taken as the starting point. The reproductive 

 process is largely influenced by what may be said to be a 

 nervous force, so far as regards animals whose functions 

 are all controlled by the nervous system. It is different in 

 the lower forms of life, as in those species which reproduce 

 by a simple process of division, or as it is commonly termed, 

 fission, or separating into two parts, each precisely alike. 

 This is the principle on which all the lower organisms repro- 

 duce themselves. A complete organism simply produces a 

 dividing membrane, which when complete forms one of the 

 walls of each of the two parts into which it separates, and 

 the two, then completed forms, again repeat the process, 

 thus prolonging the life of the race indefinitely. In this in- 

 stance heredity is perfect and paramount, and each now 

 form is precisely like the parent of it. It is the same with 

 those plants that grow from slips or cuttings, or from 

 tubers, which are in fact a part of the plant itself. And yet 

 in these there is frequent variation as in the potato, or the 

 dahlia, which as it is termed, sports and varies from the 

 original. But in animals, while there is a process extremely 

 like the fission or duplication of the lower organisms, yet the 

 action and influences of the nervous forces come in play, 

 and affect the fetus in its interuterine growth, and thus we 

 have variations in animal' reproduction which, at the same 

 time, interfere with or aid the efforts of the breeder, giving 

 him in the latter instances a new departure which he is often 



