ORGANS OF DIGESTION. 347 



tiles. There appear to be three pairs of salivary glands of 

 unequal lengths, extending along the sides of the oeso- 

 phagus, in the scolopendra gigantea, besides two poison- 

 glands placed along the lower maxillee, which send their se- 

 cretions to the two strong piercing grooved articulated hooks 

 situated at the base of the jaws. From the elongated form 

 of the stomach in the scolopendrae, the two wide extended 

 biliary follicles have a low entrance into the alimentary 

 canal, as in most insects. The stomach has the same broad 

 elongated form in the iulus, where it is followed by a short 

 small intestine, and a more wide and lengthened colon 

 marked internally with transverse folds, and the biliary 

 tubular follicles enter the lower end of the stomach. The 

 single gastric cavity of the lithobius also receives, at its 

 valvular pyloric extremity, the terminations of the two bi- 

 liary tubes which extend forwards in a tortuous manner 

 towards the head, and are supported by a small ligament 

 at their closed anterior end. So that the two long terminal 

 cceca of the stomach of the leech have now assumed the 

 form of lengthened tortuous biliary vessels, as in the highest 

 winged insects, and they here open into the lower end of 

 the chylific stomach,, as in most of the animals of that class. 



XL Insect a. The digestive organs have arrived at a high 

 degree of development in insects, and already present, in an 

 embryo-state, almost all the assistant chylopoietic organs of 

 the highest animals, as the liver, the salivary glands, the 

 pancreas, and many other parts important in the process 

 of assimilation. They vary much, however, in their form 

 and extent of development according to the consistence and 

 the nutritious quality of the food, the peculiar living habits 

 of the species, and the condition of the animals with regard 

 to their metamorphosis. The mandibulate forms of the 

 masticating organs are best adapted for comminuting hard 

 substances, and the 'tubular form or proboscis for sucking 

 food in a soft or fluid state, but even suctorial insects re- 

 quire some form of these hard parts to pierce the surface 

 from which they are to obtain their liquid food. The mouth 

 of insects is furnished with an upper and lower lip (labrum 

 and labium), a pair of strong proximate mandibles arid a pair 

 of exterior maxilke which move transversely. The labium 

 and the maxillee support each a pair of palpi ; the dense pos- 



