1914] Longevity of Insects 337 
the formulation of his theory. It was also found by Child 
(11) that the older a Planarian is, the more likely fission i. e., 
formation of a new individual from a part of the old is to take 
place. This is probably due to the greater isolation that the 
tail region of the animal has, because of the clogged condition 
of the cells as age advances. 
An application of these results of Childs, Godlewski and the 
late experiments of Loeb (32) and Lillie on permeability of 
membranes will make possible an explanation of all the results 
of these experiments. 
It must be remembered in the first place, and above all that 
one factor of the experiment was starvation—second, that the 
insects were placed first for two days at a preliminary tempera- 
ture and then at a different temperature until they died. Since 
the result of starvation at a temperature is to clear the cell of 
cytoplasmic obstacles to a certain degree. The preliminary 
treatment of an insect with starvation at a temperature will 
determine to a great extent the results of treatment at a second 
and different temperature. On the accompanying Chart II, 
I have therefore plotted, the rates of senescence. They were 
obtained by finding the value of each day at a certain tempera- 
ture for completion of a phase but since the end of this period 
was death, they may serve as the measure of the degree of sen- 
escence. 
Since death will finally be the result of physiological sen- 
escence, due to lack of food, we must bear in mind the distinc- 
tion between this and natural death which is the result of 
morphological senescence, the reverse of which is taking place 
in this case. 
Reference to this chart then, will show the degree to which 
any treatment of temperature will result in combined morpho- 
logical rejuvenation and physiological senescence. It will be 
seen :— 
1. That preparation at a high or low temperature will 
result in a combination of physiological oldness and morpho- 
logical youngness which will make the insect more liable to 
live, if it be placed in any other temperature, longer than if it 
had been living constantly at this secondary temperature. 
2. That preparation at a medium temperature will render 
the insect older, both morphologically and physiologically and 
