56 Mr. F. Merrifield on effects of temperature 
temperature corresponding to the mean of the fluc- 
tuating one. 
Again, in reference to the known English mean tem- 
peratures of the spring and summer months, it must be 
borne in mind that these are shade temperatures, and 
are below, and under certain circumstances of exposure 
or absence of cloud considerably below, those to which 
objects exposed to both sunshine and shade under natural 
conditions would be subjected. 
In the experiments hereafter described, the pup were 
exposed to the different temperatures in nearly all cases 
within a day or two, and often within a few hours, after 
pupation. The pupal period in which the temperature 
has been found to be in general most effective as regards 
the colouring is that which intervenes between the 
central inactive stage and that in which the colouring 
of the imago begins to be perceived in the pupa. 
P. napt.—It is well known that this species is season- 
ally dimorphic, the most so of the three British species 
of Pieris. Professor Weismann (‘ Studies in Heredity,’ 
by Professor Meldola) has recorded some experiments 
upon the summer brood, the result of which was that by 
exposing the pupa for a period of three months to a tem- 
perature of about 33° F. it was converted into the spring 
form, and, as might have been expected, my results are 
in general accordance with his, but with some difference 
of detail, more particularly in relation to the temperature 
during the latter part of the pupal stage, a point to 
which no particular importance seems formerly to have 
been attached. 
Mr. Vine sent me, on the 20th May last, a pair taken near 
Hailsham. They paired once or twice afterwards, and eggs to the 
number of 32 were laid on a potted plant of Cardamines, on which 
the larve were fed. These hatched in about a week, and 31 pupated 
from the 19th to the 28th June. Four pupe were placed at 90°, 
these emerged in 6 days; four more were exposed to the tem- 
perature of the room, averaging about 67°, and three of them 
emerged in from 12 to 13 days, one going over till next spring. 
There is no considerable difference between these two lots, which 
I shall therefore class together as 7 brought out at a high summer 
temperature. The remaining 23 were placed at 33° for from three 
to four months, and then divided, 12 being exposed to a tempera- 
ture averaging 54°—about equal to the shade temperature of an 
