334 TEXT-BOOK OF ENTOMOLOGY 



passage out of the duct and into the mouth by a pumping apparatus 

 furnished with special muscles. (Krassilstschik.) 



In the Odonata acinose glands are present in the imago, but not 

 in the nymph until in its last stage, Poletaiew accounting for 

 their absence in the earlier stages by the fact that the larva swal- 

 lows more or less water while taking its food. 



In the Coleoptera, as we have observed in Anopthalmus, there 

 are three pairs of salivary glands (Fig. 74). In the Blapsidee these 

 glands consist of many ramifying tubes united on each side of the 



FIG. 826. Acinous salivary glands of Orthezia cdlapliracia. In some acini the nuclei and 

 boundaries of the cells are shown. After List, from Field s Hertwig. 



oesophagus into a single duct ; in others they are but slightly 

 developed, while in still others they are wanting. 



The salivary glands are most highly differentiated in the Hymen- 

 optera, and especially in the bees (Bombus and Apis), where Schie- 

 menz found not less than five systems of glands (Fig. 329 ; also 87), 

 of which four systems are paired. One pair of these glands lies in 

 the tongue, three in the head, and one in the thorax. 



System I is situated in the head, and consists of unicellular glands ; the duct 

 from each cell leads into a common, strongly chitinized duct, opening into the 

 gullet. 



System II, composed of acinose glands, lies also in the head ; its duct is 

 united with that of System III, situated in the thorax. (Fig. 320, 2.3.) 



System IV is situated at the base of the upper surface of the mandibles, and 

 forms a delicate sac lined within with glandular cells ; its duct opens at the in- 

 sertion of the mandibles. 



System V lies in the beak, and is a single gland consisting of unicellular 

 glands ; it opens into the common opening of Systems II and III. This system 

 is wanting in the honey-bee, but occurs in Bombus and other genera. 



