620 



ZOOLOGY 



SECT 



tracheae. In the Spiders there are either four pulmonary sacs 

 (Fig. 515), or two pulmonary sacs and a system of tracheae (Fig. 516). 



c ^3-g 



iWl 



ffi 



S-8S.J 



>*: 9, x > 



.apt 



: .3 oc o to 



Tracheae are present in the Phalangida and also in the majorit 

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



