260 Pearl and Surtace 
pure lines, it is only a statement of fact to say that all the experimental 
evidence we have is against this.” 
The bulk of the evidence which has developed up to the present 
time in favor of the view that there is not a definitely accumulative 
effect following the continued selection of fluctuating variations has 
been obtained from experiments on plants. There have been practically 
no systematic investigations of the effect of selection continued through 
many generations on higher animals, but it obviously is a matter of 
the greatest importance, both theoretically and practically, to determine 
in how far the principles which have been found to hold with reference 
to selection in plants also apply with reference to animals. The 
thorough investigation of the selection problem by Jennings referred 
to was, to be sure, carried out on an animal form, Paramecium, 
The method of reproduction in this protozoan form (fission) is. 
however, so different from sexual reproduction in vertebrates, that 
it must make one cautious (as Jennings himself is) about generalizing 
too extensively from these results. What is needed is a special 
investigation of the selection in a higher vertebrate. By preference 
this should be a domestic animal, because of the obviously great 
practical importance of questions involved. So far as we are aware 
the investigations which form the subject of the present paper, 
constitute the first experimental study of the effect of selection in 
a higher animal to be carried out with large numbers of individuals 
through a number of generations and with exact numerical records 
of the character studied in each individual. 
Plan of the Experiments. 
It is our purpose to discuss the results of two distinct and 
separate but supplementary experiments. These may be designated 
as follows: 
I. Experiment in continued selection of fluctuating variations 
in fecundity. 
II. Experiment regarding the inheritance of fecundity. 
I. Experiment in continued selection of fluctuating 
variations in fecundity. In 1898 there was begun at the Maine 
Agricultural Experiment Station an experiment to determine whether 
egg production in the domestic fowl could be increased by the 
continued selection of the highest egg producers as breeders. This 
experiment was planned and started by Director C. D. Woods and 
the late Professor G. M. Gowell. An exact record was made of the 
