PHYLUM ARTHROPODA 



669 



tracheae. In the Spiders there are either four pulmonary sacs 

 (Fig. 553), or two pulmonary sacs and a system of tracheae (Fig. 554). 



M 



ff) 73 03 



."bo H 



03 73 



> rf 



!- O .vT 



o j= - 



. 



. 2 H 



sr.: a 



-, 



."_^o o 



a 



T* '** . h^ 



ft or B^ -~ 

 w^ a"^ 



-tJ <41 



2'S-~ "<l 

 &" S ~ 



rH bC : ^ D 



o ,; ..-K w 



C S. : , 

 a ~~ 53 



llll 



r - 



5 8s on . H 

 ^ a; j a 



3 1 . &o 



5^ s ^9 



-S-3 .Ig-g 



' M "S O - ^ 

 S "g -S ^ 



..fl-S 



-S3 



- aJ o 



S^ 



E9 



^ ^ 2 

 ^ a ^ 



rt c -? 



^J .?5 %S . ~ 



2 S-* 3 S 



illcl 



^^- -x 



?^-~ 



e* ^ ST 3 



e = Ss in 



Tracheae are present in the Phalangida and also in the majority 

 of the Acarida. In the Xiphosura the organs of respiration are 



