(i xi 
than those conducted by Mr. Merrifield, they had yielded 
results which were in every way confirmatory of those 
described by the latter observer. Concerning the variation 
in the period of larval life Mr. Poulton thought it probable 
that, just as dimorphism or polymorphism in colour and 
appearance was beneficial to the species by giving it an extra 
chance against its enemies, so dimorphism or polymorphism 
in the duration of life was advantageous in giving the species 
an extra chance of a favourable season as regards climate or 
prevalence of enemies. Mr. Poulton could quite endorse 
Mr. Merrifield’s observation that when an individual pos- 
sessed the tendency towards a rapid or a protracted develop- 
ment, it had a great power of resisting those conditions of 
temperature which tended to modify the rate of its develop- 
ment. This observation pointed towards the conclusion that 
the variation was innate in the individual, and was doubtless 
predetermined in the egg from which it developed, and was 
not produced by any of the surroundings in the larval or 
other states. Mr. Poulton congratulated the author upon his 
results, and trusted that the experiments would be continued. 
Prof. Meldola said that this was the first successful experi- 
ment in the way of modifying the seasonal forms of a British 
seasonal dimorphic species that had been carried out in this 
country. Such results he had long been waiting for, and he 
congratulated Mr. Merrifield upon the thoroughly pains- 
taking manner in which he was carrying on the investigation. 
Referring to Prof. Weismann’s theory of seasonal dimorphism 
Prof. Meldola said that the dark form must, in accordance 
with this view, be regarded as the ancestral form retained 
from the Glacial Period, and that artificial refrigeration had 
a tendency to cause reversion to this darker type. The 
reason why the Glacial form was the more darkly coloured 
was a question quite distinct from the present line of inquiry, 
but he could not help repeating the opinion which he had 
already expressed elsewhere, that the darker coloration had 
been acquired (through natural selection) because of the 
advantage conferred upon the species in enabling the indi- 
viduals to make the most of the sun’s radiant energy, at a 
time when the atmosphere was probably highly charged with 
