20 MILLIPEDES 



marked ability to push by the motive force of the legs. By this 

 means the animals achieve either head-on burrowing into leaf 

 mould, or push with the dorsal surface of the back into splits in 

 wood, spaces under bark and other specialised habitats. The habit 

 of curling the body into a protective spiral has been a second 

 factor of major evolutionary importance. The necessary power for 

 this pushing is achieved by the use of gaits in which the backstroke 

 of the limbs is of very much longer duration than the forward 

 stroke. These gaits require the presence of very many legs to each 

 metachronal wave and this has been achieved by the evolution of 

 numerous diplo-segments. Although moderate fleetness has been 

 evolved many times, particularly in the Colobognatha and Poly- 

 desmoidea, fast gaits usually appear to be of lesser significance to 

 millipedes than the slow, powerful gaits. Some species of lulidae 

 can on occasion make use of an unusual escape reaction. Instead of 

 curling up, they writhe the body in a series of undulating flexions, 

 wriggling rapidly through the grass or vegetation without using 

 their feet at all (Fryer, 1957 etc). 



This habit appears to be an incidental accomplishment, however, 

 and has not been of evolutionary significance. More important is 

 the ability to climb smooth rock surfaces at any angle found in 

 Polyzonium germaniciim and among the other Colobognatha, which 

 are also adapted for pushing in stony places. This climbing habit 

 necessitates a powerful grip by the opposite legs of a pair and pos- 

 sibly the use of adhesive coxal sacs when the animal is at rest. 

 Various specialisations exist for strengthening the skeleton and 

 for resisting telescoping at the inter-ring joints (Manton, 1954). 

 This may well be the explanation for the unusual solidity of the 

 millipede cuticle which is hardened not only by phenolic tanning 

 as in insects and Arachnids, but also by the deposition of calcium 

 as in the Crustacea (Cloudsley-Thompson, 1950b). 



From a physiological point of view dependence upon moist and 

 humid surroundings is one of the most important factors in the 

 lives of millipedes, as of woodlice, centipedes and other myriapods. 

 For example, it has been shown that Oxidus (Paradesmus) gracilis^ 

 a tropical species widely distributed in glasshouses in temperate 

 regions, and the 'spotted snake millipede' Blaniulus guttulatus, are 

 stimulated by drought and come to rest only in moist places 



