10 



INTRODUCTION. 



The Alimentary Canal. 



The organs of nutrition in insects consist of the intestinal canal 

 and its appendages. Except very rarely in the case of certain 



Fig. 6.— Dytiscus marginalis, male, opened from the back, a, cesopbagus or 

 crop ; h, proventriculus or fore-stomach ; c, ventriculus or mid-intes- 

 tine, with hair-like cascal glands, passing into the long intestine (ileum, 

 colon, and rectum) : the fine threads represent the Malpighian tubes ; d, 

 much developed cascal appendage : e, reservoir for secretion of anal gland ; 

 /, hind tarsus ; i, dilated joints of anterior tarsus ; o, femur ; r, gedeagus ; 

 vhm, extensor muscle of hind leg ; dr, accessory gland ; ho, testis ; B ] B , 

 B 3 , apodemes, or processes supporting the divisions of the thorax. It will 

 be noticed that the ganglia (lying close to B 3 and B. 2 ) show considerable 

 concentration. (After Graber.) 



