LEPIDOPTERA. 145 
diate and hind legs. Then it has only to raise and straighten the 
five rings which had formed the loop, and to advance its head to 
a distance equal to the length of five segments. ‘The step is thus 
made, the caterpillar making the same movements in taking the 
second and following steps. 
This sort of gait has gained for them the name of Geometers, 
because they seem to measure the road over which they travel. 
When they make a step, they apply the part of their body which 
they have just curved up to the ground, in exactly the same 
way as a land surveyor applies his chain to it. 
These looper caterpillars cannot shorten nor lengthen their seg- 
ments at will, as other caterpillars, but only bend their bodies. There 

Fig. 100.—Caterpillar of the Canary-shouldered Thorn ( Zugonia alnarza). 
are many species whose bodies are cylindrical, stiff, and of the same 
colour as bark. Their attitudes deceive even the close observer. 
They embrace the stem of a leaf or twig with their hinder and 
intermediate legs, whilst the rest of their body, vertically elevated, 
remains stiff and immovable for hours together. Fig. 100 shows 
the caterpillar of the Canary-shouldered Thorn (Eugonia alniaria) 
in this strange position. Now this is a feat of strength which 
the most skilful of our acrobats, ordinary and extraordinary, 
1, 
