234 PRINCIPLES OF POULTRY BREEDING 



The most extensive statistical work which has been carried on 

 in America is that which was done at the Maine Station from 1898 

 to 1907. Here the practice was followed of breeding continuously, 

 year after year, from the heaviest layers, regardless of all other 

 considerations except vigor and health. The final results of this 

 mass selection, after nine years' work, did not show that mass 

 selection from high producers of eggs, on the basis of the trap-nest 

 records of the individuals, brought about continuous improvement 

 in the average flock production, or that the progeny from the 

 heaviest layers were better producers than those from birds selected 

 from the general flock. These maybe considered "negative results." 



The genotype conception of heredity, on the other hand, lays 

 down the fundamental truth, firmly based on breeding experience, 

 that two sorts of variations can be distinguished : 



1. Those variations that are represented in the germinal matter, 

 and are inherited without substantial modifications, as in pure lines. 



2. Those characters that are somatic * are not inherited. This 

 group is not connected with germinal matter, but with the soma 

 or body proper. 



It is only possible by actual breeding tests to ascertain to just 

 which group a given variation belongs. 



The keynote to this latter conception of inheritance of fecun- 

 dity comes from the analysis of individual pedigrees, by which 

 method the behavior of each individual in inheritance can be de- 

 termined. The leading thought in this new conception is, that 

 the germ cell (egg or sperm) and not the body (or soma) is the fac- 

 tor of primary importance in generation. For example, the indi- 

 vidual's body (somatic) characteristics are not determined by the 

 body characteristics of its parents, but by the composition or con- 

 stituents of the parental germ cells or gametes. Thus the size of 

 a hen is not determined by the size of its parents, but by the 

 gametic construction of the latter. Recent practical applications 

 of this conception of the inheritance of fecundity have shown: 



1. That the gametic make-up of the male is of greater im- 

 portance than that of the female; since, in the average flock, the 



*"For the student not familiar with the technical terms of biology it may 

 be said that somatic is a term used to designate those characters of the organ- 

 ism which pertain to all parts except the reproductive or germ cells. The 

 reproductive cells are called gametes, and the adjective gametic means per- 

 taining to germ cells, in opposition to somatic, which means pertaining to 

 any or all parts of the organism other than the germ cells." 



