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599 
the interior. Once there, the slender lissom shape is useless, and 
it now changes to a thickish grub with a delicate sucker-mouth, 
which it applies to the body of the luckless bee-larva, whose juices are 
thereby gradually absorbed without any perceptible wound being inflict¬ 
ed : when this treatment has lasted about a fortnight nothing remains 
but an empty skin. The fly-larva, now fully grown, remains quiescent 
for some months (cf. fig. 390) and then changes to a pupa, which like 
the other stages shows a remarkable fitness for meeting the requirements 
of its position. 
Of these the most pressing is obviously the necessity of ultimately 
being able to escape from its stout clay prison-cell, and for this end the 
pupa is furnished with six hard and strong spines on the head used for 
demolishing the surrounding masonry, and some horns and thick bristles 
on the tail and body. The pupa is thus enabled to break its way to the 
open air, and the fly then emerges, leaving the pupa skin still fixed in the 
wall of the keeks cell. 
These successive adaptations to changing conditions recall other 
cases of “ hypermetamorphosis, ” such for instance as that undergone 
Fig. 391 —Pupa-skins of Hyperalonia in nest of 
SCELIPHRON X 2. 
by some of the Blister beetles ( Cantharidce ), and it is interesting to notice 
that the mode of life is very similar in these two insects, the beetle-larvae 
being parasitic on locusts andHymenoptera, just like the fly-larva whose 
career we have sketched above ; both of them, as minute and active 
individuals, start life fasting, so that in the end they may win through to 
