CH. V] THE ALIMENTARY AND EXCRETORY SYSTEMS 101 



The boundary between fore and mid-gut is marked by the zone 

 of invagination of the gizzard, which projects into the anterior end 

 of the mid-gut (fig. 46). The boundary between the mid and hind-gut 

 is marked by the entry of the Malpighian tubules, which open into 

 the alimentary canal at the extreme anterior end of the hind-gut. 

 The following table shews the principal divisions of the alimentary 

 canal in the larva and imago: 



Region Division In Larva In Imago 



/Buccal cavity and (Undivided, without (Undivided, with 

 Pharynx | salivary glands { salivary glands 



Gizzard (or Pro- 

 l ventriculus) 



T, T .J (Annular Zone 



Mid-gut | Digestive Zone 



(Small Intestine or (Short Intestine I TT ,. ., , 

 ( Ileum 1 Pre-rectal Ampulla (Undivided 



Hind-gut -^ (Branchial Basket 1 j 



I Rectum < Anal Chamber or \ Undivided 



VAnus [ Vestibule 1 



The relative lengths of these parts in larva and imago differ 

 very greatly, chiefly because of the difference in the lengths of the 

 segments containing them. Thus, for example, the mid-gut, normally 

 contained in abdominal segments 3-6, is the shortest region in 

 Anisopterid larvae, but the longest in all imagines (cf. fig. 44 A and B). 



As our present knowledge of the alimentary canal in Dragonflies 

 is principally derived from a study of the larva, and as its structure 

 also presents more points of interest in the larva than in the imago, 

 the following account will be understood to apply chiefly to the larva. 

 The more important differences in the imago are noted at the end of 

 each section. 



The Fore-Gut. 



1. Buccal Cavity and Pharynx. 



The mouth-parts, which properly form part of the digestive system, 

 in so far as they prepare the food by chewing, have been already 

 dealt with (chap. n). Within the mouth is a wide undivided cavity, 

 bounded above by the labrum and epipharynx (p. 14), below by the 

 labium and hypopharynx (p. 17), and laterally by the jaws. The 



1 Only in Anisopterid larvae. In Zygopterid larvae the rectum is undivided. 



