90 Mr. Merrifield's incidental ohsercations 



applied and so long only, it being taken up again sharply 

 the moment the change is made from the low tempera- 

 ture to the higher one. [I add some detail on this 

 point, as it seems to indicate either that extreme cold 

 as applied to the pupae of the summer emergence does 

 not absolutely arrest the development during the period 

 of its application, but allows it to go on slowly so as to 

 shorten the rest of the period, or else causes the 

 development to be more rapid after the icing ceases. 

 The first experiments, of which I have a full record, 

 were with illumiria, and the low temperature in this 

 case ranged only from about 40" to 44°, the pupae not 

 being close to the ice. On the 7th June I took for icing 

 11 males which had spun up at known dates from 30th 

 May to 7th June, and 3 females which had spun up at 

 known dates between 1st and 7th June. On the 16tli 

 June I added to them 6 males and 9 females which had 

 spun up at known dates from 4th to 8th June. All were 

 of the same brood, and had been forced up to the time 

 of removing them to the ice-box. The cooling in this 

 case did not produce any change of colour, or, if any, it 

 is a very slight one. As removed from the ice-box they 

 w^ere replaced in the forcing-box. As compared with 

 those which had remained there all the time, the average 

 period in pupa, exclusive of the days in the ice-box, was 

 as follows : — 



The record as to the illiistraria is not so fully kept. 

 These were iced 15 days, and kept at a steady tempera- 

 ture of 33"" — 34°, tlie moths, as a result, being noticeablij 

 darker in hue. I can only get a general average of the 

 time of spinning up, which I assume to be the same for 

 iced as uniced, the former having been taken pro- 

 miscuously ; and, though 1 have a record of the uniced 

 that emerged next day, my only record as to the iced is 

 that all emerged from the 4tli to the 7th August, except 

 2, which appeared on the 9th. The figures tiierefore are 

 worth but little ; such as they are, they incline in the 

 same direction as those of the illunarin, l)ut in a much 

 slighter degree. 



