122 



ENTOMOLOGY 



FIG. 152. 



C- 



two salivary ducts into a common, or evacuating, duct ; a pair 

 of salivary reservoirs (Fig. 153) may be 

 present, and the glands are frequently 

 branched or lobed, and, though usually 

 confined to the head, may extend into the 

 thorax or even into the abdomen. 



Many insects have more than one pair 

 of glands opening into the pharynx or 

 oesophagus ; thus the honey bee has six 

 pairs and Hymenoptera as a whole have 

 as many as ten different pairs. Though 

 all these are loosely spoken of as salivary 

 glands, it is better to restrict that term to 

 the pair of glands that open at the hypo- 

 pharynx. 



All these cephalic glands are evagina- 

 tions of the stomodseum (ectodermal in 

 origin) and consist of an epithelial layer 

 with the customary intima and basement 

 membrane (Fig. 154). The nuclei are 

 large, as is usually the case in glandular 

 cells, and the cytoplasm consists of a dense 

 framework (appearing in sections as a 

 network) enclosing vacuoles of a clear 

 substance the secretion; the chitinous 

 FIG. 153- 



A simple salivary 

 gland of CcEcilius. c, 

 canal; d, duct; g, g, gland- 

 ular cells. After KOLBE. 



Right salivary gland of cockroach, ventral aspect, c, common duct; g, gland; h, 

 hypopharynx; r. reservoir. After MIALL and DENNY. 



