SUBPHYLUM ARACHNIDA 



223 



their strongly proteolytic external digestion ; all but the chitin 

 of a fly is dissolved by saliva which is injected into its body, 

 and only liquid is taken into the spider's mouth. 



UNGUIS 

 PAT U RON 



TARSUS 

 TIBIA 

 PATELLA 



FEMUR 



TROCHANTER 

 COXA 



PEDICLE 



LABIUM 

 MAXILLA 



FEMUR 

 PATELLA 

 TIBIA 



■ -METATARSUS 



— TARSUS 

 CLAWS 



LUNG 



EPICYNUM 



SPINNERETTES 



Fig. 156. — Dorsal (A) and ventral (B) surfaces of spider. The ' maxilla ', or 

 gnathobase of the pedipalp, is not homologous with the maxilla of other 

 arthropods. — From Savory, British Spiders, 1926. Oxford. 



Other arachnid classes are the Scor- 

 pionidea or scorpions, with the 

 opisthosoma divided into meso- and 

 meta-soma ; the Acarina, or mites 

 and ticks, and the Phalangida or 

 harvestmen, with greatly elongated 

 legs. Many of the Acarina are blood- 

 sucking ectoparasites of man or his 

 domestic animals, important because 

 of the diseases which they carry ; 

 the ticks Ornithodorus mouhata on 

 man and Boophilus annulatus on cattle 

 carry relapsing fever and Texas fever 

 respectively, both diseases being 



::itrT 





vs 



Fig. 157. — A diagram of a 

 vertical, longitudinal sec- 

 tion through a lung-book. 



U.S., Air space; /., anterior end; 

 h., hinder end ; //., ' leaves ' of 

 book in which the blood flows ; 

 o., opening, on v.s., ventral surface 

 of body. 



