786 PROCEEDINGS OP THE AMERICAN ACADEMY. 



3. The cross-breds produced by the mating, B 9 X A £, are all of 

 high productiveness. 



4. The cross-breds produced by a mating A 9 X B $ are usually, 

 but not always, of high productiveness. 



5. The children of both sorts of cross-breds (see 3 and 4) are some of 

 high productiveness like race B, others of low productiveness, like race A. 



6. Low productiveness is inherited after the manner of a Mendelian 

 recessive character in certain of the crosses made, skipping a generation 

 and then reappearing. In other cases it has failed to reappear in gener- 

 ation Fo, indicating its complete extinction by the cross. In a few cases 

 it has failed to be dominated by high productiveness in generation F v 

 In such cases the female parent has always been of race A. Hence low 

 productiveness (or sterility) of the female may be transmitted directly 

 through the egg from mother to daughter, but only indirectly through 

 the sperm, the character skipping a generation. 



7. A cross between two races, one inbred for thirty or more genera- 

 tions and of low productiveness, the other inbred for less than ten 

 generations and of high productiveness, produced offspring like the latter 

 in productiveness, but not superior to it. 



8. The same two races crossed after an additional year of inbreeding 

 (about twenty generations) produced offspring superior to either pure 

 race in productiveness. 



9. Inbreeding does not affect the variability in number of teeth on the 

 sex-comb of the male, nor the variability in size. 



10. Size of the male individual is closely correlated with number of 

 teeth in the male sex-comb. 



Bibliography. 

 Bos, [J.] R. 



'94. Untersuchungen iiber die Folgen der Zucht in engster Blutsverwandt- 

 schaft. Biol. Centralbl., Bd. 14, pp. 75-81. 

 Crampe, H. 



'83. Landwirtsch. Jahrbiicher, Bd., 12, p. 421. 

 Guaita, G. von 



'98. Versuche mit Kreuzungen von verschiedenen Rassen des Hausmaus. 

 Ber. naturf. Gesellsch. zu Freiburg, Bd. 10, pp. 317-332. 

 Fabre-Domengue, [P.] 



'98. Unions consanguines chez les Colombins. L'Intermediaire des Bio- 

 logistes, torn. 1, p. 203. 



