46 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 8 1 



of each gnathal sternum enters into the hypopharyngeal region. Riley 

 (1904) descrilies the hypopharynx of Blatclla germanica as formed 

 in the embryo from the sterna of the mandibular, first maxillary, and 

 second maxillary segments. 



In the more generalized pterygote insects, the hypopharynx hangs 

 like a tongue in the preoral cavity (fig. 19, Hphy) behind the mouth 

 (Mtli), shut in anteriorly by the labrum, laterally by the mandibles 

 and maxillae, and posteriorly by the labium. Its base generally extends 

 posteriorly to the labium (figs. 18 D, 19), and in the groove between 



Mth 



-4 



Lin Slin 



Fig. 20. — The hypopharynx. 



A, three-lobed hypopharynx of an ephemerid nymph, with ventral adductor 

 muscles of mandibles (KLh) attached to its base. B, head of embryo of Amirida 

 maritima (from Folsom, 1900), ventral view, showing median lingua (Lin) 

 and paired superlinguae {Sliii) that combine to form hypopharynx of adult. 

 C, transverse section through mandibles of embryo of Tomocerus plmnbcns 

 (from Hoffman, 1911), showing origin of superlinguae (Slin) from inner 

 angles of mandibles. D, hypopharynx of Microccntrum rhoinbifolmiii, ventral, 

 with rudiments of suspensorial arms (HS) on which ventral mandibular ad- 

 ductors (KLh) are attached. 



the two organs is situated the orifice of the salivary duct [SLO) . In 

 general, therefore, the salivary orifice serves as a landmark for sep- 

 arating the hypopharynx from the labium, or for determining the 

 hypopharyngeal region when a specific hypopharyngeal lobe is lacking, 

 as in the honeybee ; but the opening of the salivary duct may be at the 

 apex of the hypopharynx, as in Homoptera, or, when the hypopharynx 

 and labium are united, as in many insect larvae (fig. 54 A, D), it may 

 lie at the tip of the combined labio-hypopharyngeal structure. 



In some insects the hypopharynx consists of a median part and of 

 two lateral lobes. In such cases it usually projects forward like a lower 



M 



