Is there a Cumulative Effect of Selection? 261 
egg production of each hen during the first year of her life; trap 
nests being used to furnish the individual records. In 1907 the 
records of egg production which had accumulated from the beginning 
of the experiment up to that time, were turned over to the present 
writers for analysis. The present paper sets forth certain of the 
results of the analysis made. The plan of the experiment begun in 
1898 was to make from a then superior strain of Barred Plymouth 
Rock hens, which had been pure bred for a long time by Professor 
Gowell, a continuous close and intense selection with reference to 
egg production. The practice in breeding was to use as mothers 
of the stock bred in any year only hens which laid between 
November I of the year in which they were hatched and 
November I of the following year, 160 or more eggs. After 
the first year, all male birds used in the breeding were the 
sons of mothers whose production in their first laying year 
was 200 eggs or more. Since the normal average annual egg 
production of these birds may be taken to be about 125 eggs, it 
will be seen that the selection practiced was fairly stringent. 
Close inbreeding was not practiced. It was always possible to 
avoid this, since after the first few years of the experiment the flocks 
were very large (always containing more than 500 birds and usually 
nearer a thousand). While there was no close inbreeding no “new 
blood’ was introduced into the strain from the outside during the 
period of the experiment. 
While every effort was made to preserve uniform environmental 
conditions during the course of the experiment certain unavoidable 
environmental accidents occurred in certain of the laying years. These 
accidents may be held to have affected the egg production in those 
years adversely. Therefore, in discussing the results it will be necessary 
to make certain corrections for them. For a detailed account of 
their nature as well as for further details regarding the conduct of 
the experiment the more extensive report (loc. cit.) must be consulted. 
II. Experiment regarding the inheritance of fecundity. 
In 1907 the experiment described above, having led to definite results 
was brought to an end. There was planned for 1908 a new experiment 
designed to test from another standpoint the conclusions which had 
been tentatively reached from the earlier experiment. In the conducting 
of the long selection experiment the females used as breeders were 
grouped into two classes, viz., (a) ‘‘unregistered” or birds laying 160 
