( Ixi ) 



rature of 65° or less. Alninaria pupae endured cold better 

 than autuimiaria, two moths in perfect condition having 

 emerged after exposure to 33° for fifty days ; the effect on the 

 colouring was slight, but in the direction of greater darkness. 

 Eighty-seven summer pup^ oiillustraria from a single pair were 

 taken ; fourteen of them were left at the ordinary temperature, 

 and emerged in something less than a fortnight ; the rest were 

 iced (33°), and taken out at periods successively lengthened 

 by two weeks till twenty weeks' icing had been reached, and 

 there were enough pupse left for twelve or fourteen weeks 

 more. There was a difference in colour, increasing (but not 

 regularly) as the period of icing was lengthened, a general 

 warm brownish hue prevailing, with an increase of darkness. 

 There was a striking difference, caused by the icing, in the 

 markings ; the sinuosities and angles that mark the outer edge 

 of the dark inner part of all the wings being straightened out, 

 the acute angle on the costa giving place to an obtuse angle, and 

 the outer edge forming a nearly straight line from the costa 

 continuously across both wings, and, on the posterior wing, 

 turning at a sharp angle towards the abdomen, so that the 

 shape of the dark inner part of the whole insect approached a 

 half-hexagon, instead of a half-circle. There was in this change 

 of colour and markings a general approximation to the colour 

 and markings of the natural spring emergence. 



Vigour seemed in no way affected by icing for twenty weeks 

 this pupa, which usually lived for about two weeks at a 

 temperature not lower than 65°. The reverse experiment 

 — forcing or even keeping at a temperature of about 60° the 

 autumn pupa — had a very much more injurious effect ; the 

 great majority so treated died ; those that emerged first were 

 much nearer the summer than the spring type in colouring, 

 but they grew darker (not regularly) as the time in pupa was 

 protracted, and some that were after some weeks of this 

 treatment exposed to cold wintry weather for about six weeks 

 were much darkened in colour. The experiments seemed to 

 show that, by forcing, the larva of illnstraria might generally 

 be made to assume absolutely the summer form, the j^iipa 

 only partially so, and with difficulty, and much loss ; but 

 that by icing, the pupa of the summer form might without any 



PROC. ENT. SOC. LOND., IV., 1889. K 



