376 LECTURE xvir. 



the alimentary tract presents the two distinct apertures : it is simplest 

 in the carnivorous larviform Myriapods ; presents more numerous 

 and distinct constrictions and divisions in the Hexapods, and increases 

 in complexity and length, as the food requires most preparation in 

 order t3 its conversion into the animal nutrient fluid or chyle. 



The oesophagus of the Centipede is long, and dilated posteriorly, 

 where it communicates with the stomach ; this is a small muscular 

 cavity, bent upon itself, and lined by a longitudinally plicated horny 

 membrane. The intestine is long, straight, and wide, slightly saccu- 

 lated transversely ; it contracts, and is longitudinally folded near its 

 termination. In the lulus a short and wide oesophagus expands into 

 a shorter and wider muscular stomach. This is succeeded by a long 

 and wide chylific stomach, with longitudinal folds, separated by a 

 circular linear constriction, in the posterior third of the body, from 

 the intestine : this, again, is divided by a second constriction into two 

 equal partS; the first longitudinally folded like the stomach, the last 

 puckered into short transverse sacculi, until within a little distance 

 of the anus, which is protected by a pair of horny valves. 



In the Polydesmus the oesophagus gradually expands into the long 

 chylific stomach, which is separated by a short contracted pyloric 

 tube from the intestine. This suddenly swells out to equal width 

 with the stomach, is puckered up in its posterior half by short trans- 

 verse plicae, where it first gradually, and then suddenly, contracts to 

 terminate at the anus. 



The accessory glands of the digestive tract are slender tubes in the 

 Myriapod as in the Hexapod tracheary Insects. In the Polydesmus 

 and lulus there are two such salivary glands at the sides of the oeso- 

 phagus, converging anteriorly to open into the pharynx. The more 

 compact and similarly situated poison glands, which terminate in the 

 large perforated hooked mandibles, in the Centipede, are superadded 

 to the simpler salivary glands of the Chilognatha. 



Slender biliary tubes creep upon the intestinal tunics in the Cen- 

 tipede, and pour their secretion into the canal close to the gizzard. 

 Excretory, probably urinary, tubes open into the terminal division 

 of the intestine ; and these are present in the Iulid?e. 



The alimentary tract in Hexapod Insects is divided into pharynx, 

 oesophagus, ingluvies or crop, gizzard, chylific stomach, small intes- 

 tine, caecum, and rectum. Ail these parts rarely co-exist in the same 

 insect. The oesophagus is directly continued from the sucking ap- 

 paratus in Haustellate Insects without a pharyngeal dilatation. 



In the carnivorous Dragon-fly* the alimentary tract is short and 



* Prep. No. 589. 



