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SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. IIO 



median lobe (Hst) known as the hypostome. The hypostome appears 

 to be formed by the union of anterior coxal processes, and is thus 

 quite comparable to the similarly formed under lip of the Ricinulei 

 (fig. 10 C). The hypostome is the floor of the preoral cavity, and 



Fig. 22. — Acarina, structure of the capitulum. 



A, diagrammatic anterior view of the capitulum, with chelicerae cut off at 

 bases, showing lower lip, or hypostome (Hst), formed of united coxal processes 

 (compare with A of figure 2). B, diagrammatic longitudinal section of anterior 

 end of body (compare with D of figure 2). C, diagram of a primitive ixodid 

 coxa according to Schulze (1935), showing parts that may enter into the forma- 

 tion of the capitulum : a, area porosa ; an, auricle ; c, coxa ; /, coxal process ; pc, 

 processus cymatii ; s, sella ; t, trochanter. D, E, composition of the capitulum, 

 dorsal and ventral, according to Schulze (1935): ch, chelicera ; //, sternum; 

 k, part of primary cephalic lobe ; sc, subcoxa ; sch, cheliceral sheath ; u, hypo- 

 pharynx; other lettering as on C. 



its concave or grooved upper surface, more or less covered by the 

 labrum, is the preoral food canal of the Acarina. 



A lengthwise sectional view of the acarine capitulum (fig. 22 B) 

 shows the tectum (Ted) as the outer wall of a fold (b-c-d) extended 

 over the chelicerae, which latter thus appear to be sunken into a pouch 

 of the head wall above the epistome. By comparison with a corre- 



