144 THE INSECT WORLD. 
The variations which caterpillars present, as far as the number 
and situations of their pro-legs are concerned, are the followig :— 
The greatest number among them have ten pro-legs; others 
have only eight; others only six—these may be called semi- 
loopers; others only four, one pair being situated on the last 
ring, and the other on the ninth, as in the case of looper cater- 
pillars. And, lastly, there are others which have only two pro-legs. 
The various forms, numbers, and positions of these organs, produce 
great differences in the mode of locomotion of caterpillars. Those 
provided with ten or eight membranous legs have in walking 
only a very slight undulating motion. Their bodies are parallel 
to the plane which supports them. They can walk very quickly ; 
but their steps are short and quickly repeated. Others, on the 
contrary, in proportion as the number of their false legs diminish, 
and the spaces between the legs increase, walk in a more irregular 
and quaint manner. 
If the reader will glance at Fig. 97, taken from Réaumur’s 
“‘Memoire sur les Chenilles en général,’’* which represents a looper 
caterpillar, with four mem- 
branous legs, he will see that 
there is a considerable space 
between the posterior legs and 
the first pair of pro-legs, along 
which the body has no points 
of support. If one of these caterpillars, lying quiet and at full 
length, determines to walk, in order to take its first step (Fig. 98) 
it begins by humping its back, curving into an arch that part which 
has no legs, and finishes by assuming the position seen in Fig. 99. 

Fig. 97.—Looper Caterpillar. 

Fig. 98.— Caterpillar curved into an arch. Fig. 99.—Caterpillar at full length. 
In the former position it has its two intermediate legs against the 
posterior legs, and, in consequence, it has brought forward the 
hinder part of its body, a distance equal to the interval of the five 
segments which separate them. There it hooks on by its interme- 
* Tome 1., p. 49, Plate i., Fig. 6. 
