The Glow-Worm and Other Beetles 



and belly; Instead of the useless legs of the 

 thorax, it has a walking-apparatus almost re- 

 sembling feet, which appear, contrary to 

 every rule, on the dorsal surface. 



The first seven segments of the abdomen 

 have, both above and below, a four-sided 

 facet, bristling with rough protuberances. 

 This the grub can either expand or contract, 

 making it stick out or lie flat at will. The 

 upper facets consist of two excrescences sepa- 

 rated by the mid-dorsal line; the lower ones 

 have not this divided appearance. These 

 are the organs of locomotion, the ambulacra. 

 When the larva wishes to move forwards, it 

 expands its hinder ambulacra, those on the 

 back as well as those on the belly, and con- 

 tracts its front ones. Fixed to the side of 

 the narrow gallery by their ridges, the hind- 

 pads give the grub a purchase. The flat- 

 tening of the fore-pads, by decreasing the 

 diameter, allows it to slip forward and to 

 take half a step. To complete the step, the 

 hind-quarters have to be brought up the same 

 distance. With this object, the front pads 

 fill out and provide support, while those be- 

 hind shrink and leave free scope for their 

 segments to contract. 



With the double support of its back and 

 belly, with alternate puffings and shrinkings, 

 190 



