86 



THE CLASS OF INSECTS. 



tine, and the colon and whim. The latter part, as well as the 

 crop and proventriculus, are sometimes absent. 



Of the appendages of the canal, the first 

 are the salivary glands, which are usually 

 long simple tubes, which in the larva, ac- 

 cording to Newport, form the silk vewlx. 

 They " empty themselves by a single duct 

 through the spinneret on the floor (labium) 

 of the mouth." In the Ant-lion (Myrmeleon) 

 the silk is spun from " a slender telescopic- 

 like spinneret, placed at the extremity of 

 its body," and AVestwood also states that the 

 larva of Clirysopa spins a cocoon "from the 

 spinneret, at the extremity of the body." 



These silk glands Avhen taken out of the 

 larva, just as it is about ready to transform, 

 are readily prepared as "gut" for fish-lines, 

 etc., by drying on a board. 



In the Bees these glands are largely de- 

 veloped to produce a sufficient amount of 

 salivary fluid to moisten the dry pollen of 

 Fig. 45. flowers, before it enters the oesophagus. 



"Bee-bread" consists of pollen thus moistened and kneaded 

 by the insect. The Honey-bee also dissolves, by the aid of the 

 salivary fluid, the wax used in making its cells. Newport 

 believes this fluid is alkaline, and forms a solvent for the other- 

 wise brittle wax, as he has seen this insect " reduce the per- 

 fectly transparent thin white scales of newly secreted wax to 

 a pasty or soapy consistence, by kneading it between its man- 

 dibles, and mixing it with a fluid from its mouth, before apply- 

 ing it to assist in the formation of part of a new cell." 



Insects have no true liver ; its functions being performed 

 u by the Avails of the stomach, the internal tunic of which is 

 composed of closely-aggregated hepatic cells." (Siebold.) In 

 the Spiders and Scorpions, however, there is a liver distinct 

 from the digestive canal. In the Spiders it is very large, 

 enveloping most of the other viscera. 



FIG. 45. Alimentary tube of Corydnlus cornutus. a, oesophagus; b, proven- 

 triculus; c, ventriculus; rf, large intestine; e, urinary tubes; /, coecum; g, testisor 

 ovary. From Leidy. 



