THE CAPRICORN 47 



expands its hinder ambulacra, those on the back as well 

 as those on the belly, and contracts its front ones. Fixed 

 to the side of the narrow gallery by their ridges, the hind- 

 pads give the grub a purchase. The flattening 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 dis- 

 tance. With this object, the front pads fill out and pro- 

 vide support, while those behind shrink and leave free 

 scope for their segments to contract. 



With the double support of its back and belly, with al- 

 ternate puffings and shrinkings, the animal easily ad- 

 vances or retreats along its gallery, a sort of mold which 

 the contents fill without a gap. But if the locomotory 

 pads grip only on one side progress becomes impossible. 

 When placed on the smooth wood of my table, the animal 

 wriggles slowly ; it lengthens and shortens without ad- 

 vancing by a hair's-breadth. Laid on the surface of a 

 piece of split oak, a rough, uneven surface, due to the 

 gash made by the wedge, it twists and writhes, moves the 

 front part of its body very slowly from left to right and 

 right to left, lifts it a little, lowers it and begins again. 

 These are the most extensive movements made. The 

 vestigial legs remain inert and absolutely useless. Then 

 why are they there? It were better to lose them alto- 

 gether, if it be true that crawling inside the oak has de- 

 prived the animal of the good legs with which it started. 

 The influence of environment, so well-inspired in endow- 

 ing the grub with ambulatory pads, becomes a mockery 

 when it leaves it these ridiculous stumps. Can the struc- 



