INSECTS AT LARGE 



32!) 



mally found in any animal, are also found in 

 them, though these may vary considerably 

 as to shape and size. For example, those 

 insects which feed on vegetation have longer 

 digestive tracts than do those feeding on 

 animal matter. 



The parts of the digestive system (Fig. 

 214, E) are: The mouth or buccal cavity; a 

 slender oesophagus, dilated to form a thin- 

 walled crop; a muscular gizzard or proven- 

 triculus, a glandular stomach or ventriculus 

 from which little pouches or caeca branch 

 out, and a long slender intestine. At the 

 junction of the stomach and intestine the 

 slender Malpighian tubules discharge their 

 excretions into the alimentary canal. 



Contrary to the higher forms of life no 

 air-breathing insects have lungs. They re- 

 ceive their oxygen through a network of 

 tubes, called tracheae which open through 

 little spiracles ( ) along 



the sides of abdomen and thorax (Fig. 215). 



If, therefore, one wished to chloroform 

 or drown an insect it could not be done by 

 covering the head or placing the head un- 

 der water. The abdomen and thorax would 

 have to be covered with the anaesthetic or 

 the water. 



Fig. 213. 



I. External anatomy of Calopte'nus spre'tus, the head and thorax disjointed; 

 up, Uropatagium ; /, f urcula ; c, cercus. (Drawn by J. S. Kingsley). 



II. An adult mosquito, much enlarged, with all the parts that are used in classi- 

 fication named. (Smith, N. J. Experiment Station, Bulletin 171, 1904). 



III. Side view of Locust with the Thorax separate from the head and abdomen 

 divided into three segments. (I, III, from Packard's "Zoology," by permission of 

 Henry Holt & Co.) 



If the insect flies a great deal these tracheae are expanded into air 

 sacs, which adds to the lightness of its body. 



