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 



dr 



ho- 



FIG. 320. nyticus marginalia, <$, opened from the back : a, crop ; b, proventricuhis ; c, mid- 

 intestine beset with fine coecal glands; d, long ciecal appendage of the colon ; Jl^-Ji^, apodemes ; 

 vhm, coxal 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, ?; 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- 



