207 
If one leaves the abnormal high mortality of 53.7 °/, of the first 
series out of consideration, the average egg mortality over the two 
experiment years of 58468 eggs becomes 32.4 °/). 
As the outcome one may therefore assume that, in general, only 
2/3 of the number of eggs are hatched. 
b. The mortality among the larvae. 
As has been said, the cause of the egg mortality is still uncer- 
tain; that of the larvae mortality gives more positive indications. 
Fortunately epidemics have not appeared up till now. So they cannot 
have played a part in the mortality figures mentioned below. The 
larvae gnaw at each other’s bodies and perhaps they sometimes eat 
each other up entirely; this cannibalism is, to be sure, the main 
cause of the larvae mortality. 
A small percentage not gnawed at, died of unknown causes. 
The larvae mortality in the experiments years 1915/1916 and 
1916/1917 was: 
Number of Lar- Dead Larvae Morta- 
_ Year of experiment. \vae the culture ' lity in 100 
wot. “Larvae. =<) 
was begun with, larvae. 
1915—1916 11986 | 3655 30.4 0/0 
1916 — 1917 11294 1983 iy ea 
Totals and average. 23280 | 5638 24.2 Ofo 
| | 
Here the opposite case to that of the egg-mortality presents itself, 
viz. the first experiment year shows a considerably bigher mortality 
figure than in the second year. 
A factor that may have influenced this lies in the circumstance 
that an addition of thin fresh cut slices of potato or carrot scattered 
on the food (enhancing the humidity) had a specially favourable 
effect, not only on the growth and development of the larvae, but 
particularly on the mortality of the pupae. With regard to this, 
convincing figures will be submitted when the pupae mortality will 
be treated. 
In consequence of the results obtained in the early part of 1917, 
the addition of slices of potato was started late, when a large part 
of the total number of pupae obtained of that experiment year had 
been already gathered. By this the late gathered pupae (together 
