366 The Pedigree of Insects 



has but little value as a sign of their relationships. 

 But there is no improbability in the idea that the 

 class may have arisen from the fourteen-legged 

 animals indicated above as the progenitors of insects, 

 the head with five pairs of appendages being common 

 to both classes. Among the insects, however, there 

 has been a tendency towards reduction in the number 

 of the body-segments •, among centipedes towards an 



increase (fig. 1 80). 

 No undoubted centi- 

 pedes are known 

 earlier than Oligocene 

 times, but in the Car- 

 boniferous group 

 (Protosyngnatha) 

 which is believed to 

 represent their pro- 

 genitors, the number 

 of body-segments 

 was fewer than in liv- 

 ing forms (203). 



Diplopoda. — The 

 Millipedes (Diplo- 

 poda) d i if e r from 

 _ „ ^ . , r? r "^T-ii- ^ Insects in having 



Fig. 180.— Centipede Fig. i8i.— Millipede o 



{Rhysidarugulosa, {P latyrhachu s apparently Only thrCC 



Poc). Half natural mu-andus, Poc). . r , 



size. Half natural size. pairS Of appCUdagCS 



After Pocock in Weber's " Zool. Ergeb Niederl. on the head of the 



Ost-Indien." i 1 • ^ r r 



adult mstead or rour; 

 these are the feelers, the mandibles, and a plate-like 

 lower lip, formed by the fusion of a single pair of 

 maxillge (though according to some authorities two 

 pairs are present). The number of body-segments is 

 large and variable ; for the most part they become 

 fused together in couples so that each apparent 

 segment bears two pairs of legs (fig. 181). Fossil 



