THE INTERNAL ANATOMY OF INSECTS 



109 



(c) Neuroptera. Myrmeleonidae, Osmylidae, Sisyridae, and 

 Chrysopidae. In these families the larvae spin silk from the anus. 



(d) Coleoptera. In the Campodeiform larvae of Stylopidae and 

 Meloidas. 



b. THE FORE-INTESTINE 



The layers of the fore-intestine. The following layers have been 

 recognized in the fore-intestine : 



The intima. This is a chitinous layer which lines the cavity of 

 the fore-intestine; it is directly continuous with the cuticula of the 

 body-wall ; and is molted with the cuticula when this is molted. 



The epithelium. This is a cell layer which is continuous with the 

 hypodermis; it is sometimes quite delicate so that it is difficult to 

 demonstrate it. 



The basement membrane. Like the hypodermis the epithelium is 

 bounded on one side by a chitinous layer and on the other by a base- 

 ment membrane. 



The longitudinal muscles. Next to the basement membrane there 



is a layer of longitudinal muscles. 

 The circular muscles. Out- 

 side of the longitudinal muscles 

 there is a layer of circular 

 muscles. 



The peritoneal membrane. 

 Surrounding the alimentary 

 canal there is a coat of con- 

 nective tissue, which, is termed 

 the peritoneal membrane. This 

 is one of a few places in which 

 connective tissue, so abundant 

 in Vertebrates, is found in in- 

 sects. 



The regions of the fore- 

 intestine. Several distinct reg- 

 ions of the fore-intestine are 

 recognized; but the extent of 

 these regions differ greatly in 

 different insects. 



The pharynx. The pharynx 

 is not a well-defined region of the 

 intestine; the term pharynx is commonly applied to a region between 

 the mouth and the oesophagus; in mandibulate insects the pharynx 



sd 



Fig. 125. Longitudinal section through 

 the head of Anosa plexippus, showing 

 the interior of the left half; mx, left 

 maxilla, the canal of which leads into the 

 pharynx; ph, pharynx; o, oesophagus; 

 m, m, muscles of the pharynx; sd, 

 salivary duct (After Burges). 



