238 NATURAL HISTORY OF WASPS. 
susceptible of the injurious influences of alternations 
of heat and cold, dry and wet, particularly when the 
swarm is too weak to temper these alternations. 
This constitutes the great difficulty in experiments 
on wasps, which involve a constant or frequent ex- 
posure of the comb. And it vitiates the conclusions 
from them; for, under such unfavourable conditions 
the development of the brood may be delayed or 
entirely prevented. At least this has been the case 
in all my experiments on this subject, with whatever 
care they were conducted. Up to the last moment 
when the new-born insect emerges from her cell the 
pupa is more or less dependent on the kind offices 
of her elder sisters. The larve, of course, must be 
wholly dependent on them for their hourly supplies 
of food. But the pups have wants even in their 
closely sealed cells, which only wasp-nurses can 
anticipate. The temperature must be attended to, 
and the atmosphere must be kept at the proper 
degree of moisture. And for want of hourly atten- 
tion to these particulars, the experiment will fail, or 
lead to false conclusions. Sometimes my wasps 
mildewed, but more commonly they got too dry, and 
when they did crawl out at last, they appeared with 
shrivelled wings. They were perfect in all other 
respects, but quite useless either as citizens or as 
specimens, with these little black stumps of pinions. 
The wing could be spread out in warm water, almost 
Miihlhausen, and to any insects rather than wasps; so I can only 
generally refer to them on the present occasion. But I may cite his 
authority in confirmation of what has been said above of the mach 
greater delicacy of insects in the larval than in any other stage of 
their existence. ‘Die Abhiingigkeit der Insecten von Ihrer Umge- 
bung.’ 8vo Leipzig, 1867. 
