Eruciform Larvae 



107 



often much longer than the body of the larva wherein 



they lie folded. They secrete a sticky fluid, which, 



after pressure in the spinneret, is forced out through 



the duct as a double, flattened thread of silk. Each 



of the three thoracic segments bears a pair of short 



legs with hard chitinous feet and claws ; these 



legs correspond, of course, with those of the 



perfect insect, from which, however, they differ 



immensely in form. The first, second, seventh 



and eighth abdominal segments are limbless, but 



the third, fourth, fifth, 



sixth, and ninth each carry 



a pair of short, stumpy 



"prolegs" — cylindrical in 



shape and armed at the tips 



with incomplete circles of 



booklets. Clasping the 



twig on which it rests with 



its prolegs, the caterpillar 



stretches out the front part 



of its body and grasps, with 



its thoracic legs, a point 



further in advance. Then 



the prolegs disengage their 



clasp; by contraction of the 



body lengthwise they are 



drawn forwards to seize 



the twig again at a point nearer that where the thoracic 



legs are holding. Thus by successive stretching and 



shrinking of its body, brought about by the action 



of longitudinal bands of muscles in each segment, 



the caterpillar goes on its way in search of food. 



Such a soft-skinned, worm-like grub is known as 

 an eruciform larva, and this type prevails among the 

 most highly developed insects — the Moths, Flies, Ants 

 and Bees for example. Very considerable modifica- 



Mn 



Fig. 67. — Head of Goat-moth Cater- 

 pillar (Cossus) from behind. 

 Magnified. W A feeler ; il/«. man- 

 dible : jl/x. Tst maxilla; ; Z.;«. 2nd 

 maxilla; with spinneret. After 

 Lyonnet, from Miall & Denny. 



