268 MR. F. BALFOUR-BROWNE ON THE [ Mar. 2, 
sluggish, showing but little interest in the Paramecia with which 
they were abundantly supplied. 
In the beginning of December, seeing that matters were at a 
standstill, I placed 18 of the tumblers ina Hearson incubator and 
maintained a fairly constant temperature of 19° C. (66°2° F.), 
which isa very high summer temperature. The outer door of the 
incubator was removed, so as to admit light, but, from the position 
in which the incubator stood, the occupants had little more than 
twilight even on the brightest days. 
The effect of the warmth was soon obvious, as all the nymphs 
in the incubator showed great activity and readiness to feed. 
One nymph moulted 8 days after being placed in the incubator, 
and others followed fairly soon. By the end of February several 
of the nymphs had completed their 8th stage, while one was 
through its 9th and another through its 10th. During the same 
time the nymphs, some fifty and more, in the ordinary tempe- 
rature of the laboratory did not moult at all, with the exception 
of three specimens, two of which moulted at the beginning of 
December and the other at the end of February. The average 
length of the nymphs in the incubator was 11:0 mm., while that 
of those outside was 2°7 mm. ! 
A large part of the experiment had now to be sacrificed, as I 
was leaving Norfolk for Ireland, so the incubator was gradually 
cooled off and the former occupants became less active and much 
less hungry. On April 20th I started a similar incubator in 
Larne, and this was kept going until July 10th, but only one or 
two of the nymphs which had been kept warm during the winter 
were placed in it, a number of the less advanced ones being 
selected in order to further test the effects of temperature. The 
new batch of nymphs quickly showed great activity and keen 
appetites and began to grow rapidly, moulting at short intervals. 
If further evidence were needed of the effect of temperature in 
the causing of moults, it is to be found in the cases of three 
nymphs, one in the 5th and two in the 6th stage, which had 
stagnated for 92, 135, and 104 days respectively through the 
winter. They were placed in the incubator for 21 days in 
February. Each moulted 7 days after being warmed, and each 
moulted a second time in the next 10 days. After being removed 
from the incubator one moulted three weeks later, while the 
other two were five weeks without changing. 
This effect of temperature upon the duration of the stages 
makes it impossible to find a fair average duration for any stage 
except by using only those nymphs which have been incubated, 
and only those stages passed through while in the incubator. 
Unfortunately, this was not foreseen, so that the material at hand 
is very meagre. I have, however, prepared a table showing for 
19 nymphs the number of days occupied by each stage, indi- 
cating the days passed in the incubator by using a thicker type 
(v. Table 1). 
From Table 1, reading down the columns and only using the 
figures for stages begun and completed in the incubator, we can 
