DIVISIONS OF THE ALIMENTARY TRACT 101 



The alimentary tract in the adult insect is divided into a number 

 of parts, each of which is more or less specialized for a particular 

 function. The arrangement in the Diptera does not 

 differ much from what is found in other insects, except 

 in the details of structure, and the homology of the parts is as a rule 

 easily made out. The parts may be enumerated as follows : 



The Buccal cavity, with the epipharynx and 

 hypopharynx. 



, r The Pharynx. 



Developed from the _, _ , 



< The Oesophagus. 

 Stomodaeum. | _, _ r , 



The Crop, or food reservoir. 



The Proventriculus, homologous with the 

 gizzard of insects which take solid food. 

 Developed from the j The Mid . gut 

 Mesenteron. I 



/ The Intestine, or Hind-gut, which may be 



Developed from the divided into a proximal part, the Ileum, 



Proctodaeum. | and a distal part, the Colon. 



I The Rectum. 



The three divisions are also known as the fore-gut, mid-gut and 

 hind-gut respectively. It should be noted that these terms have a 

 definite morphological significance, and are not to be used merely with 

 reference to position. In the Muscid flies the term ' Intestine ' is 

 applied to a part of the mesenteron ; confusion will not arise if the 

 position of the Malpighian tubes is kept in mind. 



In addition, there are two sets of structures accessory to the aliment- 

 ary tract, namely, the salivary glands, connected with the stomodaeum, 

 and the Malpighian or urinary tubules, inserted into the proctodaeum. 

 All the above parts can be distinguished in the Diptera. As regards 

 the length of the canal, there is a progressive increase, and a tendency 

 to the formation of a tube with a uniform diameter throughout, as 

 one passes from the simpler Orthorrapha to the Cyclorrapha, and 

 at the same time an increase in the length of the salivary glands. 

 In the Culicinae the alimentary tract when drawn out is only a little 

 longer than the body of the fly, while that of Musca is three or more 

 time the length. 



The buccal cavity and the pharynx have already been described 

 in connection with the mouth parts. Together they form the sucking 

 apparatus by which the food is drawn from the wound up the canal in 

 the proboscis and passed on to the oesophagus. 



