lilOH SCHOOL ZOOLOGY. 



205 



body. The walls of these tubes are delicate, but tlioy are pre- 

 vented fi-oui collapsing by the i)reseuce of a strengthening, s[>iral, 

 chitinous fibre, just as, in the higher Verteln-ates, the windpipe 



is by its cartilages. 

 They are, therefore, 

 called tracheae, and 

 the air-breathinsr Ar- 

 thiopods are hence 

 frequently si)oken of 

 i^" = | as the "tracheate" in 

 "^aZl contradistinction to 

 the " branchiate" Ar- 





O .SJ3 



2 = - , 



3 p O - 



|H.|| thropods. Two groups 



c-f r-2 of the tracheate Ar- 



•'^-jjS thropods remain for 



c^^'l us to discuss — the 



1 1 1 ^ Insecta and the Myri- 



= £l o apoda. Althouijh the 



•r-^'.<2i ^^tter contains the 



"5 3.::.^ most primitive forms, 



S?^S yet some knowledge 



J'g |£. of a very accessible 



^ 2 = = member of the former 



sS~o class — the red-legged 



°'~=^ grasshopper — will 



n ?^. 2 serve to introduce to 



o ..2 



both. 



20. Among sever- 



££-J?i ^1 species of locusts 



which are abundant 





"' I" in the fields in the 



CO "C — 



r-4 ~ — ^ 



there is none 



2 s easier to obtain than 



species above 



o H o 



" .T3 



h1 the 



