INHERITANCE OF FECUNDITY 159 



discussed above and the physiological basis, which has been 

 designated the normal ovulation factor. 



It is a fact well known to poultrymen, and one capable of easy 

 observation and confirmation, that different breeds and strains 

 of poultry differ widely in their laying capacity. In saying 

 this the writer would not be understood to affirm that a definite 

 degree of fecundity is a fixed and unalterable characteristic of any 

 particular breed. The history of breeds shows very clearly that 

 certain breeds now notably poor in laying qualities were once 

 particularly good. One of the best examples of this is the Polish 

 fowl. But, in spite of this, inheritable breed and strain differences 

 in fecundity exist, and probably always have existed. Such 

 inheritable differences are independent of feeding or any other 

 environmental factors. Thus the strain of Cornish Indian Games 

 with which I have worked are poor layers, regardless of how they 

 are fed or handled. This is merely a statement of particular 

 fact; it does not imply that there may not exist other strains of 

 Cornish Indian Games that are good layers. 



The difference between this strain of Cornish Indian Games 

 and Barred Plymouth Rocks, when kept under the same condi- 

 tions and managed in the same way, is shown in tables 1 and 2, 

 which give the frequency distributions and constants respectively, 

 for flocks of these breeds kept at the Maine Station. The birds 

 included in table 1 were all pullets, hatched at approximately the 

 same time, and reared, housed, fed and cared for in all respects 

 similarly. The Plymouth Rock distribution includes birds of 

 both high and low fecundity stra'ns. The low producing 

 birds lower the mean in what is really an unfair manner, so far 

 as concerns breed comparisons. The point is that, in the work of 

 the Station, low-producing lines have been propagated for experi- 

 mental purposes to a much greater extent than would be the 

 case in purely random breeding of the Maine Station's stock, 

 the Barred Plyinouth Rock breed. To make a perfectly just 

 comparison between Cornish Indian Games and Barred Rocks, 

 thS strains of the latter deliberately bred for low egg production 

 should be excluded. It has, however, in the present case been 



