MILLIPEDES 



23 



test its nature by means of the sensory hairs and chemo-receptive 

 sensillae referred to. 



Ahhough to milHpedes, as to woodUce and to the other myria- 

 pods, humidity is the most important factor of the environment, 

 these animals are not able to find their way directly to damp 

 places: instead, they are merely repelled by drought. Nevertheless 



0-05 

 mm 



Fig. 7. Sense organs of the millipede Oxidus gracilis. Left, 

 antenna and below the seventh and eighth segments more highly 

 enlarged to show peg and cone sensillae. Right, gnathochilarium 

 or lower lip with one of the palps more highly magnified to show 

 peg-organs. (After Cloudsley-Thompson, 195L) 



this stereotyped and curiously negative behaviour is surprisingly 

 effective in preventing them from w^andering aw^ay from their nor- 

 mal habitats: but it does raise the problem of how dispersal can 

 take place and new habitats become colonised. 



There are a number of cases on record of millipedes, sometimes 

 accompanied by centipedes, and woodlice migrating in vast armies. 



