HEREDITY IN THE PROTOZOA 287 
“the difference produced by selection continued to 
exist after conjugation.”’ It appears that some kind 
of change had been produced, and that the change 
in rate was inherited after selection ceased. 
More recently still Jennings (1916) has carried 
out an elaborate experiment with another Protozoan, 
Difflugia corona (Fig. 66). This form also shows 
“in nature” great variability, due, it appears, to 
several or to many races often existing in the same 
locality. If any individual is taken as the starting 
point for a new population, it is found that the 
fission line that results is composed of individuals 
that are more like the parent than like members of 
the wild population taken as a whole. In other 
words each individual tends to transmit its peculi-. 
arities to its offspring, Fig. 67. Jennings then 
showed that selection within a pure line, 7.e., in a 
population descended from a single individual by 
fission, brings about a change in the direction of 
selection and that this change remains at least for a 
time after selection ceases. 
The characters that were examined included the 
number of spines, the length of the spines, the 
diameter of the shell, the depth of the shell, the 
number of spines around the mouth, the diameter 
of the mouth. Through selection many diverse 
lines were produced in a strain coming from one 
original individual. The selection was based not 
only on individual differences, but also on ‘past 
performance.” 
Selection was often made by picking out extreme 
