314 TEXT-BOOK OF ENTOMOLOGY 



the adults. In Hymenoptera it has been found in ants and wasps, 

 but is absent in Cynipidae, Ichueumonidae, and Tenthredinidae. All 

 those insects (including their larvae) possessing this funnel eat solid, 

 indigestible food, while those which do not possess it take fluid 

 nourishment. It is elastic, and firmly encloses the contents of the 

 digestive track. Until Schneider's discovery of its general occur- 

 rence, it had only been known to exist in the viviparous Cecidomyia 

 larvae (Miastor). Wagner, its discoverer, noticed in the stomach of 

 this insect a second tube which contained food. Pagenstecher was 

 inclined to regard the tube as a secretion of the salivary glands. 

 Metsclmikoff, however, more correctly stated that the tube consisted 

 of chitin, but he regarded it as adapted for the removal of the secre- 

 tions. (Schneider.) Plateau, however, as well as Balbiani, the latter 

 calling it the " peritropic membrane," considers this membrane as a 

 secretion of the chylific stomach, and that it is formed at the surface 

 of the epithelial cells. It surrounds the food along the entire diges- 

 tive tract, forming an envelope around the faecal masses. On the 

 other hand, Gehuchten states that in the larva of Ptychoptera its 

 mode of origin differs from that described by Plateau and by 

 Schneider, and that it is a product of secretion of special cells in the 

 proveiitriculus. 



The mid-intestine. - - This section of the digestive canal, often, 

 though erroneously, called the " chylific stomach " or ventriculus, 

 differs not only in its embryonic history, but also in its structure 

 and physiology from the fore and hind intestine of arthropods, and 

 also presents no analogy to the stomach of the vertebrate animals. 

 In insects it is a simple tube, not usually lined with chitin, since it 

 is not formed by the invagination of the ectoderm, as are the fore 

 and hind intestine, the absence of the chitinous intima promoting 

 the absorption of soluble food. Into the anterior end either open 

 two or more large coecal tubes (Fig. 299), or its whole outer surface 

 is beset with very numerous fine glandular filaments like villi 

 (Fig. 317 and Fig. 329). 



The mid-intestine varies much in size and shape ; it is very long 

 in the lamellicorn beetles (Melolontha and Geotrupes), and while in 

 Meloe it is very large, occupying the greatest part of the body-cavity, 

 in the longicorn beetles and in Lepidoptera it is very small. The 

 pyloric end consists of an internal circular fold projecting into the 

 cavity. In the I'socidae (Csecilius) the pyloric end is prolonged into 

 a slender tube nearly as long as the larger anterior portion. 



The limits between the mid and hind intestine are in some insects 

 difficult to define, the urinary tubes sometimes appearing to open 



