316 TEXT-BOOK OF ENTOMOLOGY 



in front of the circular fold. It is the same with the Malpighian tubes. They 

 are not, therefore, he claims, dependences of the terminal intestine, but of the 

 mid-intestine. lieauregard has observed tlie same thing in the vesicating insects 

 (Meloidse). The Malpighian tubes, he says, open into the "chylific stomach" 

 before the valvular crown. This arrangement does not seem to be general, 

 because, according to Balbiani, the Malpighian vessels open into the beginning 

 of the intestine in Cryptops. Compare also Minot's account of the valve in 

 locusts separating the stomach from the intestine, and in front of which the 

 urinary or Malpighian tubes open. 



Histology of the mid-intestine. The walls of the stomach are com- 

 posed of an internal epithelium, a layer of connective tissue, with two 

 muscular layers, the inner of which is formed of unstriated circular 

 muscular fibres, and the outer of striated longitudinal muscular 

 fibres. 



In the cockroach short processes are given off from the free ends of 

 the epithelial cells, as in the intestine of many mammals and other 

 animals. " Between the cells a reticulum is often to be seen, especially 

 where the cells have burst ; it extends between and among all the 

 elements of the mucous lining, and probably serves, like the very 

 similar structure met with in mammalian intestines, to absorb and 

 conduct some of the products of digestion." (Miall and Denny.) 



Gehuchten shows that the epithelial lining of the meseiiteron 

 (chylific stomach) of the dipterous larva Ptychoptera is composed of 

 two kinds of cells, i.e. secreting or glandular cells and absorbent 

 cells, the former situated at each end of the stomach, and the 

 abdominal cells occupying the middle region. The part played by 

 these cells in digestion will be treated of beyond in the section on 

 digestion. (See p. 327.) 



The hind-intestine. In many insects this is divided into the 

 ileum, or short intestine, and the long intestine. The limit between 

 the intestine and stomach is externally determined by the origin of 

 the urinary tubes, which are outgrowths of the anterior end of the 

 proctodaeum. Like the fore-intestine the hind-intestine is lined with 

 a thick muscular layer, and, as Gehuchten states, the passage from 

 the epithelial lining of the stomach (mid-intestine) to the muscular 

 lining of the intestine is abrupt. 



Large intestine. In Ptychoptera, as described by Gehuchten, 

 there are no precise limits between the small and large intestine ; 

 the epithelium of the large intestine has a special character, and its 

 constituents present a close resemblance to the absorbed cells of the 

 chylific stomach, being like them large and polygonal. The muscu- 

 lar layer is not continuous, and is formed of longitudinal and circular 

 fibres, the latter being the larger. 



