PHYLUM ARTHROPOD A 229 



of the body and are then designated as a beak or rostrum. 

 Though the typical number of legs is four pairs, the newly 

 hatched young usually have but three pairs (Fig. 108 C), and in 

 one family (Eriophyidae) only two pairs are present in the adults. 

 The Acarina are of great biological importance. As parasites 

 of man and of other animals they have great economic signifi- 

 cance, and particularly the ticks, as carriers of disease-producing 

 organisms, have received considerable attention. The southern 

 cattle tick (Boophilus annulatus, Fig. 108) is the carrier of the 

 organism (a protozoan, Babesia) which causes Texas fever or 

 tick fever in cattle. The cattle industry in the South is greatly 

 hampered by outbreaks of this disease. Through misunder- 

 standing of the status of the generic name Boophilus, this tick has 

 been referred to frequently in literature under the name Magaro- 

 pus. The itch mites {Sarcoptes scabei, Fig. 109) burrow within 

 the skin of man and produce a disease known 

 as the itch. Mites of poultry and of other 

 birds and of mammals also belong to the 

 Acarina. The water mites (Hydrachnida) 

 usually live as free adults in water, though the 

 larvae are frequently encountered as parasites 

 on molluscs, insects, and other animals. 



IV. Other Orders of Arachnida 



There are a considerable number of small, Fig. i0 9. — An 

 though very sharply marked, groups of ^^^^^ mite, Sar- 



'^ "^ '^ "^ 7 o 1 copies humams . 



arachnids members of which fail to come {After Banks). 

 within the foregoing descriptions of the larger 

 groups. These are frequently recognized as comprising several 

 independent orders. Chief of these are the Pseudoscorpionida. 

 the Solpugida, the Phalangida, and the Linguatulida. 



The pseudoscorpions resemble the scorpions except that 

 there is no differentiation of pre- and postabdomen and no sting. 

 The chelicerae function as spinning organs. Chelifer is a com- 

 mon genus. 



The Solpugida are comparatively rare. The head bears 

 a pair of extremely large chelicerae which serve for crushing the 

 prey and long, leglike pedipalps which seem to function chiefly 

 as feelers. The first thoracic segment is fused with the head, 

 but the remaining three are free. The genus Eremobates is 

 represented by several species in the southern United States. 



