DOMESTIC ANIMALS 



33 



position strongly suggest their zebra 

 sire, others their respective dams; but 

 even the most zebra-like in form are 

 utterly unlike their sire in their mark- 

 ings." A "curious blending of charac- 

 ters, derived apparently partly from their 

 actual and partly from their remote an- 

 cestors" was observed. 



Mendel's law — At present the most 

 widely exploited theory regarding the 

 behavior of hybrids is that of Mendel, 

 originally published in 1865, and re- 

 cently applied by many observers to ex- 

 plain the facts of plant and animal 

 hybridization. According to Mendel's 

 law one-fourth of the hybrids after two 

 generations resemble one parent, one- 

 fourth the? other parent while one-half 



encies are intermixed the mixture is 

 only temporary and not stable. In other 

 words, if these animals are used for 

 breeding purposes, their offspring are 

 likely to revert to the pure form of one 

 or the other breeds from which they de- 

 scended. Again, when the sire and dam 

 are of very different character, the pro- 

 geny may revert to the original wild 

 form and thus all the advantages of pre- 

 vious breeding be lost. 



Sports — Variation in farm stock is 

 usually a slow process due to the accu- 

 mulation of minute differences. Occa- 

 sionally a great leap or mutation occurs 

 giving rise to what is known as a sport. 

 Striking examples of this are to be found 

 in the ancon sheep which suddenly orig- 



Fig. 22 — MODERN TYPE BERKSHIRE SOW 

 (Weight 45<; pounds at 13 months) 



are of mixed nature and are constantly 

 separating into the pure parent forms 

 during subsequent generations. Mendel 

 first worked on the common garden pea 

 and his law has not been found to hold 

 good in all cases of the hybridization of 

 plants, much less in all animal hybrids. 

 Crossing — Enough is known concern- 

 ing the behavior of offspring of very 

 dissimilar parents to show that crossing 

 of different breeds is of little value in 

 the hands of the average farmer. The 

 results cannot be predicted. Two sets 

 of tendencies are mixed together, but 

 there is no likelihood that the offspring 

 will show any advance on either parent. 

 Moreover, it appears that when very un- 

 like and more or less antagonistic tend- 



inated in Massachusetts in 1791, and in 

 the black-shouldered peacock. In these 

 two instances the sports bred true and 

 reproduced their characters perfectly in 

 their offspring. Sports are usually more 

 prepotent and stable than mere varia- 

 tions which closely resemble the parent 

 form but they are not always transmis- 

 sible. 



Telegony i s a term used to denote the 

 supposed influence of a previous sire on 

 the offspring of the same dam by an- 

 other sire. It has also been called in- 

 fluence of a previous impregnation or 

 infection and numerous examples of its 

 supposed occurrence are reported in the 

 literature of the subject. Many cases 

 have been reported of children from a 



