THYSANURA. 



65 



bearing upon the question of the use of the antennae 

 that these organs are longer in the cave-inhabitins 

 species, Campodea Cookei, than in 

 the species that Hve in the Hght. 



The mouth parts consist of 

 one pair of mandibles and two 

 pairs of maxillae ; but as these 

 are used only upon soft substances, 

 they are much simpler and weaker 

 than those of the locust, and less 

 freely movable. It has already 

 been pointed out ^ that they are 

 of generalized structure, and that 

 the more speciaUzed mandibulate 

 mouth parts of locusts and suc- 

 torial mouth parts of butterflies 

 may have been derived from an 

 ancestor having mouth organs 

 similar to these of Campodea. 



The three pairs of legs are sim- 

 ilar in structure, since they are all 

 used in running. They are hairy, 

 and hooked at their ends, but are 

 without cushions. The simpHcity 

 of the thoracic rings indicates 

 that wings are not developed, 

 and this is the case, the adult 

 Campodea never possessing flying-organs. Each of 

 the first seven rings of the abdomen bear a pair of 

 short, jointed appendages (not shown in figure ; see 



Fig. 27. 



1 See p. 49. 



