INSTINCTIVE, BEHAVIOUR IN- INSECTS 81 
worm, barely one-twentieth of an inch in length (Fig. 13, c). 
It has three pairs of longish bristles near the anterior end, and 
a single yet longer pair at the hinder extremity. These aid 
it in creeping over the wall of the cell. Its small head is 
armed with short, stiff bristles. For many days it wanders 
over the surface of the cell, inserting its bristly head into each 
minute cranny and crack. Throughout this long period it 
‘has never a bite nor sup. Probably many of them never 
succeed in finding a crevice by which they can effect an 
entrance, but those that do manage to wriggle in undergo a 
change, lose their bristles, and develop a minute suctorial 
mouth, through which the contents of the larva are absorbed 
into their swelling bodies (Fig. 13, D). When fully grown 
they are quite helpless, and unable to get out from the cell in 
which they arenow imprisoned. For months they lie quiescent, 
but in the succeeding spring they pass into a pupal condition 
very different from that of most flies. The relatively large 
head is armed with strong spines; the middle region bears 
bristles directed backwards ; the posterior end has short spines 
(Fig. 18, £). Fixing itself to the interior of the cell by the 
latter, it strikes with its armoured head repeated blows on 
the walls of its prison until a breach is at last made, and 
sufficiently enlarged to form a suitable exit. Then the pupa- 
skin bursts, and the imago insect emerges and flies off. At 
each stage of life there is the closest relation between structure 
and behaviour, and each is equally adapted to a biological end 
of which the creature has never had an opportunity of gaining 
any experience. 
Exceedingly multifarious are the ways in which insects 
thus provide for the future of young they will never see. 
Antherophagus lives in flowers, and is believed to seize with its 
mandibles humble bees, which then unwittingly bear the 
parasitic beetle to the nests in which alone the larve have 
been found. The larve of our common oil-beetle (J/el0é) are 
parasitic on the bee, Anthophora. It deposits its ten thousand 
eggs without observable discrimination ; but the active young 
larva instinctively seizes and attaches itself to any hairy object, 
G 
