10 



SCHOOL ENTOMOLOGY 



slender tubes opening into the mouth cavity. The phar- 

 ynx narrows rapidly and merges into the oesophagus or 

 gullet. This corresponds exactly to the oesophagus in 

 vertebrates, and is merely a passageway for the food on its 

 way to the stomach. In the thoracic region the oesophagus 



Sromo 



Mid. int. 



Fn;. 6. Internal Structure of a Caterpillar. 



1. Dorsal view with upper wall removed, showing organs in place, ph, pharynx. 



2. Inner surface of upper wall showing organs of the circulatory system. A, 

 aorta; A, heart or dorsal-vessel; H.M., heart muscles or "Wings of the Heart." 



3. Digestive organs removed, exposing organs of nervous and respiratory 

 systems. Br., brain or supra-cesophageal ganglion; a.g., salivary gland; gl., 

 ganglion; Tr., Trachea; n.c., nerve cord; or central nervous system; sp., spiracles; 

 R., rectum or posterior part of the intestine. 



4. Silk gland removed. The location of the gland may be seen in the upper 

 figure. 



5. The alimentary canal, removed, oea., (Esophagus ; M.T., Malpighian 

 tubules; Mid-int., mid-intestine From photographs of an " Azoux model " of 

 the silk-worm. 



widens out into a pouch-like structure called the crop 

 which is followed by the proventriculus. Following the 

 proventriculus is the stomach proper or ventriculus. Here 

 the food is digested, much of the digestive fluid being 



