90 THB BBE-KBBPBR'S GUIDB ; 



those in higher animals. There is an inner and an outer 

 chitinous layer, and the intervening cellular or epithelial, 

 where secretion takes place. 



In those larv^ that form cocoons these are the source of 

 silk. In the glands this is a viscid fluid, but as it leaves the 

 duct it changes instantly into the gossamer thread. Bees and 

 wasps use this saliva in forming their structures. With it and 

 mud some wasps make mortar ; with it and wood, others form 

 their paper cells ; with it and wax, the bee fashions the rib- 

 bons that are to form the beautiful comb. As will be seen 

 later, these glands are very complex in bees, and the function 

 of the secretion very varied in both composition and function. 



Lfining the entire alimentary canal are mucus glands 

 which secrete a viscid fluid that keeps the tube soft and pro- 

 motes the passage of food. These lining cells also absorb, and 

 may secrete a digestive fluid. 



The true stomach (Fig. 36, s; 27 S), is very muscular; 

 and often a gizzard, as in the crickets, where its interior is 

 lined with teeth. The interior of the stomach is glandular, 

 for secreting the gastric juice which is to liquefy the food, that 

 it may be absorbed, or pass through the walls of the canal into 

 the blood. 



Appended to the anterior end of the stomach are the from 

 two to eight coeca, or, as in some beetles, very numerous villi 

 or tubules. These are believed by Plateau and others to be 

 pancreatic in function. These are not found in bees. Attached 

 to the lower portion of the stomach are the urinary or Mal- 

 pighian tubules (Fig. 27, m, t), so named from their discoverer, 

 Malpighi. There may be two to eight long tubes, or many 

 short ones as in the bees, where we find ISO. The finding in 

 these of urea, uric acid and the urates settles the matter of their 

 function. Cuvier and others thought these bile-tubules. 

 Siebold thinks that some of the mucous glands secrete bile, 

 and others act as a pancreas. 



The intestine, when short, as in larvae and most carnivora, 

 is straight, and but little, if any, longer than the abdomen, 

 while in most plant-eaters it is long, and thus zigzag in its 

 course. It is a very interesting fact that the alimentary canal 

 in the larva may be partly shed at the time of molting. 



