CHAPTER V 



THE ALIMENTARY AND EXCRETORY SYSTEMS 



As the alimentary and excretory systems of the Dragonfly are 

 closely related, both morphologically , 



and physiologically, we shall deal 

 with them together, in a single chapter. 



THE ALIMENTARY CANAL (fig. 44). 



In the Dragonfly, as in all insects, 

 the alimentary canal is formed of 

 three main regions. The most an- 

 terior of these (fore-gut] is formed as 

 an invagination of the ectoderm in 

 the region of the mouth. Hence its 

 epithelium is continuous with the 

 hypodermis around the mouth, and is 

 covered internally by a fine chitinous 

 lining or intima, corresponding and 

 continuous with the cuticle. In like 

 manner, the most posterior region 

 (hind-gut) is a similar invagination of 

 the ectoderm, and its epithelium is 

 similarly covered by a fine internal 

 chitinous intima. Separating these 

 two regions lies the mid-gut or mesen- 

 teron ("chylific stomach," "ventricu- 

 lus") formed from the endoderm. In 

 the Dragonfly it is the mid-gut alone 

 which carries on the processes of di- 

 gestive secretion and absorption. The 

 fore-gut simply serves to prepare the 

 food for digestion, while the hind -gut 

 is concerned with the removal of the waste left over. 



B 



A. 



Fig. 44. Alimentary canal of Aesch- 

 na brevistyla Ramb. A. Imago 

 (natural size). B. Larva ( x If), c. 

 Hind-gut of imago ( x 3), to shew 

 remnants of rectal gills (br'). an 

 anus ; be buccal cavity ; br bran- 

 chial basket ; cr crop ; g gizzard ; 

 il ileum ; mg mid-gut ; mp Mal- 

 pighian tubules ; ces oesophagus ; 

 pa pre-rectal ampulla ; r rectum ; 

 sg salivary glands; si short in- 

 testine; v vestibule. Original. 



