TJSE OF THE SPIRACLES. 105 



and swept across the body of the creature, it col- 

 lapses, turns on its back, and dies straightway. 

 For the oil has stopped up the spiracles, and so the 

 supply of air is cut off from every portion of the 

 body at once. The same rule holds good with all 

 insects. 



There is yet one more organ to which I must 

 draw attention, and that is the curious bag-shaped 

 object marked E. 



Just as the silk is contained in the vessel c, so the 

 saliva is contained in E, and is developed according 

 to the character and habits of the insect. Some in- 

 sects require a large supply of that liquid, which is 

 used for various purposes, and others require com- 

 paratively little. The caterpillar in which these 

 receptacles may be found best developed is the larva 

 of the Goat-moth, which may be easily found within 

 the substance of decaying trees. Of the Goat-moth 

 we may speak in a future page. 



If the reader will again refer to the engraving on 

 p. 100, he will see that between the tracheal tube 

 and the digestive apparatus is a curiously waved 

 line, forming two loops in its upper portion, and 

 running into a confused entanglement below. This 

 entanglement, however, is only apparent, for in 

 nature there is no entangling ; all is perfect in order. 



This wavy line represents one of the numerous 

 thread-like vessels that surround this portion of the 

 digestive apparatus, and are called the biliary vessels, 



