PRINCIPLES OF LIVESTOCK BREEDING. 15 



MATERNAL IMPRESSIONS. 



There is another very ancient belief which may be mentioned in 

 this connection. This is the belief that objects seen by a prospective 

 mother, especially if a nervous shock is produced, have an effect on 

 the unborn young. Such an influence appears highly improbable 

 in the light of our present knowledge, as there is no nervous connec- 

 tion between mother and offspring or even a direct blood connection. 

 The favorable evidence is all of the unsatisfactory character of anec- 

 dotes, while deliberate attempts to obtain the phenomenon have all 

 failed. The kind of case which was formerly often explained in this 

 way, such as the appearance of a red calf in a black Aberdeen Angus 

 herd, is now accounted for in other ways. 



DETAILS OF HEREDITARY TRANSMISSION. 



BLENDING AND ALTERNATIVE INHERITANCE. 



Until rather recently it was usual to consider the contributions of 

 the two parents to the heredity of the offspring to be as inseparably 

 mixed together as would be two liquids. This view is illustrated in 

 the common figure of speech used in referring to the degree of hered- 

 ity from a given stock. Thus the cross between a Merino and a 

 Shropshire sheep is spoken of as half-blood Merino and half-blood 

 Shropshire and is expected to show a blending of the two breeds in 

 all their characteristics. Another Shropshire cross produces a three- 

 quarter blood, which is expected to be intermediate in all respects 

 between the half-blood and the full-blood Shropshire. 



This simple formula is still as good as any in predicting the results 

 of a cross about which nothing is known but the characteristics of 

 the two animals which are mated, and even in a large class of cases 

 in which a great deal more is known. 



Certain cases, however, have long been known in which this fusion 

 of characteristics does not take place. This is especially likely to be 

 true of coat colors. Every one knows, for example, that a great 

 variety of sharply distinct colors — black, maltese, tabby, orange, 

 etc. — may be found within a single litter of kittens. 



The gap between sharply alternative inheritance of this kind and 

 apparent blending inheritance is bridged over by the large class of 

 cases in which the first generation of a cross is more or less of a blend, 

 but the second generation shows greatly increased variability, the 

 different characteristics of the two races tending to reappear in all 

 combinations. 



HEREDITARY UNITS. 



The basis for any kind of inheritance, of course, must oe material 

 contributed by the microscopic sperm and egg cells in their union. 

 The fundamental conception of the present theory of heredity is 



