184 PHIL RAU AND NELLIE RAU 
The St. Louis Cecropias will be discussed in detail, and the other 
groups will be taken up later only for comparative evidence. 
The mean duration of life of all the St. Louis Cecropias (under 
normal conditions only) for the three years was 10.61, 13.73 and 
7.71 days. We are at once struck with the great variation, for 
in so brief a life a day is as a decade in the life of man. If now 
we can detect the reasons for these variations from year to year 
in the life of the population, it may lead us toward the discovery 
of the factors controlling the duration of life of the species. 
In 1910 notes were based upon 178 insects froni the 205 which 
emerged, (101 males and 104 females). Hardly was the work 
begun when a marked difference in the date of emergence was 
observed. The insects of that year began to emerge on April 13, 
a month earlier than in the year before or after. 
Table 2 shows at a glance the marked correlation between the 
date of emergence and the duration of life of the animals; those 
which emerged early lived distinctly longer lives than those which 
appeared late in the season. The duration of life of the entire 
population varies from 5 to 25 days. The table clearly shows how 
all of the early emerging insects segregate to the long-lived lot, 
while those emerging late in the season fall under short lives. 
In fact, May 14 seems to be a distinct dividing line between the 
early emerging or long-lived groups, and the late or short-lived 
group. The late lot, taken separately, has practically the same 
dates of emergence and duration of life as the 1909 population. 
It certainly seems remarkable that the population should split 
up in this fashion; the problem is most perplexing. The ques- 
tions at once arise in our minds: Is long or short life hereditary? 
Is it regulated by climatic conditions? Are these results due to 
local conditions, and would the same be seen in material from 
other localities and in other species of the same family? Has 
each organism an ‘“‘allotment”’ of a certain number of days, i.e., 
from the time of the fertilization of the egg to the death of the 
adult, and is a longer or shorter period in one of the early stages 
correlated with a shorter or longer life in the imago? 
A cause for this early emergence is very uncertain to deter- 
mine without tracing the duration of the different stages of the 
whole life eyele of each insect. But the fact that this abnormally 
