Sex as an Adaptation 443 
The individuals in question, in which this interchange of 
micronuclei has taken place, undergo a change, and behave 
differently from what they did before. They feed, become 
larger and less vacuolated, and are more active. They soon 
begin once more to divide. Maupas found that an individual 
that has conjugated will run through a new cycle of divisions, 
which will, however, after a time also slow down, unless con- 
jugation with another individual having a different history 
takes place. If conjugation is prevented, the individual will 
die after a time. These results seemed to show that the 
division phase of the life history cannot go on indefinitely, 
and that through conjugation the individual is again brought 
back to the starting-point. 
Quite recently Calkins has carried out a somewhat similar 
series of experiments, which have an important bearing on 
the interpretation of Maupas’ results. The experiment of 
isolating an individual and tracing the career of its descen- 
dants was repeated with the following results: two series 
were started, the original forms coming from different locali- 
ties. Of their eight descendants four of each were isolated. 
The remaining four of each set were kept together as stock 
material. The rate of division was taken as the measure of 
vitality. The animals divided more or less regularly from 
February to July. After each division (or sometimes after 
two divisions) the individuals were separated. About the 
30th of July the paramoecia began to die “at an alarming 
rate, indicating that a period of depression had apparently 
set in, or degeneration in Maupas’ sense.’ Up to this time 
the animals had been living in hay infusion, renewed every 
few days, from which they obtained the bacteria on which 
they feed. Calkins tried the effect of putting the weakened 
parameecia into a new environment. Infusion of vegetables 
gave no good results, but meat infusions proved successful. 
“The first experiment with the latter was with teased liver, 
which was added to the usual hay infusion. The result was 
