

THE ANAL GLANDS AND VENT 



319 



a valve, serving to retain the food in the absorptive portions of the 

 digestive track till all nutriment is extracted. 



The epithelial folds of the larvae of dragon-flies serve as organs of 

 respiration, the water being admitted into this cavity, and when 



vim. 



PIG. 320. Dyticus marginalia, cf, opened from the back : <t, crop ; b, proventriculus ; o, mid- 

 intestine beset with fine coecal glands ; d, long ctecal appendage of the colon ; B t -B 3 , apodemes ; 

 rh </(. coxa! extensor muscle, moving the hind leg ; ho, testis ; dr, accessory gland ; r, penis ; e, res- 

 ervoir of the secretion of the anal gland. After Graber. 



forcibly expelled serving to propel the creature forward. Paired and 

 single anal glands (repugnatorial) enter the rectum of certain Cole- 

 optera (Figs. 302, 1-, 317, s; 320, e). 



The vent (anus). The external opening of the rectum is situated 

 in the end of the body, in the vestigial 10th or llth abdominal seg- 



