reigns in the physical constitution of each individual, and 

 must, consequently, change with it. Therefore a first essay 

 may succeed, which, renewed the following year under, 

 apparently, exactly similar conditions, may give totally 

 different results arising from imperceptible reasons far too 

 various to enumerate. We will only cite one example ; let us 

 suppose the ram to have been more fatigued during the serving 

 than the ewe during gestation and lactation, or given at an 

 adult age to young sheep, the force with which he impressed 

 his characteristics on his progeny had decreased the following 

 year by the sole fact of his having aged one year, whilst the 

 same cause acting upon the sheep have given them more 

 constancy ; in this case the produce will be inferior to the 

 preceding ones. 



Let us pass on to examine from a commercial point 

 of view the first crossing mentioned. If the breeder considers 

 it advisable to work on his crossed breed as it stands, he has 

 only to proceed no further and not change his system ; he 

 has only to procure reproductors of the two races necessary 

 for his speculation. 



So far from its being easy it is often excessively 

 difficult to obtain the animals required ; thus, to simplify 

 matters, it often happens that the breeder selects, from among 

 the animals of his first cross breedings, those which bear the 

 most analogy to each other, and whose characteristics appear 

 to be almost intermediary between those of the father and 

 mother, and allies them together with the view of forming a 

 fresh mixed breed, in which he hopes to find all the qualities 

 which induced him to make a cross. The greater part of 

 the time, it is a search after constancy* (that most precious 

 quality of race) amongst animals without breeding, and that, 

 too, when it has been destroyed amongst these same animals 

 by the very mixture to which they owe their existence. Then 

 we have continual oscillations between the characteristics of 

 the two races, and constancy will be all the more difficult to 

 procure because the two brought together at the commence- 

 ment presented less mutual analogy. 



Crossing is not always confined to the first degree as 

 we have just depicted it ; perhaps the breeder may wish to 

 pursue the three-quarter blood plan. His difficulties, whilst 

 of the same nature, are, in this case, less, because constancy 

 has been partly destroyed among the females, whereas the 

 male presents himself in all his hereditary strength. Taking 

 numbers ranging from a maximum of 100 to a minimum of o 

 to represent the hereditary strength of the reproducers 

 brought together at the first and second crossing, it will be 

 seen that the mixed breeds of the former possess each T = 5o 



* By constancy is meant the uniform transmission of the qualities which are 

 sought to be attained by the breeder. [NOTE BY TRANSLATOR.] 



