300 MAINE AGRICULTURAL EXPERIMENT STATION. I915. 



second time whose progeny froip the first year's mat- 

 ing had proven to be all high producers. Similar types 

 of selection were followed by the mediocre and low 

 lines, except that segregating families were put in the 

 mediocre class. 



3. The selection of males was along essentially the same 



lines, with only such difference as is involved in the 

 fact that the male makes no performance record him- 

 self. Males were put into the breeding pen the first 

 time on the basis of the records of their dams, on the 

 one hand, and of their sisters, on the other hand. 

 Those whose progeny proved that they were transmit- 

 ting the character to which selection was being made 

 were used a second or even third time as breeders. 



4. Complete individual pedigrees, whereby each offspring in- 



dividual's parentage, both male and female, was 

 known. 



5. The records of production of the progeny of each mating 



separately recorded and studied as a unit. 



It will be noted that there are but two essential differences 

 between the plan in this period and that followed in the earlier 

 one. These are : first and most important, that in this second 

 period the principle of progeny testing was introduced into the 

 scheme of breeding. The second difference was that selection 

 was carried on for low production as well as for high, which 

 had not been previously done. A third difference is apparently 

 found in the fact that in this second period of selection -the 

 winter record rather than the yearly record is made the basi^ 

 of selection. This is in no way an essential difference. 



As a result of the studies made in this period on the plan of 

 breeding outlined the mode of inheritance of the character 

 winter production was definitely determined, and has been con- 

 firmed by subsequent work.* The character was shown to be 

 Mendelian in its genetic behavior, depending upon two factors, 

 one of which is sex-linked. 



3. The Period from ipi2 to Date. — The only difference in 

 the mode of breeding the stock of Barred Plymouth Rocks in 



^Pearl, 1912, he. cit., also Amer. Nat., Vol. XLIX, 1915, pp. 306-317, 

 and Curtis and Pearl, Jour. Exp. Zoology, Vol. 19, 1915, pp. 45-59. 



