144 



THE INSECT WORLD. 



The variations which caterpillars present, as far as the number 

 and situations of their pro-legs are concerned, are the following: 

 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 is 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 Reaumur's 

 " Memoire sur les Chenilles en general/'* 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. 93. 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 i. p. 49, Plate i. Fig. 6. 



