144 



almost invisible in the fully distended state, when 

 the cells are much flattened. 



The nucleus of these cells is large and centrally 

 situated. The chromatin is arranged in small 

 stellate masses arranged circumferentially and 

 centrally, and connected with one another by 

 fine threads of chromatin. There is a body which 

 stains less deeply, generally to be made out 

 (karyosome) in the centre of the nucleus. 



Occasionally young cells are to be seen near 

 the basement membrane. 



The muscular coat is very thin. It consists 

 of an open mesh-work of long muscular fibres 

 running longitudinally and circularly. In the 

 large posterior portion of the mid-gut, these fibres 

 form a very regular series of large square or 

 rhomboidal meshes. In the narrow anterior 

 portion they are more closely approximated, so 

 that the muscular layer here is more evident in 

 sections. 



The individual muscle fibres are very long, 

 fusiform, striated fibres. On the outer surface of 

 the mid-gut lie numerous large branched cells in 

 which the small tracheae end, and from which 

 bundles of minute structureless air tubes pass into 

 the wall of the mid- gut. These cells are frequently 

 well shown in gold chloride specimens. Similar 

 cells occur throughout the viscera in connexion 

 with the tracheal endings (See 'Tracheal Endings'). 



The Homologue of the Proventriculus. — Mention 

 has been made of a fold occurring at the anterior 

 extremity of the mid- gut. This consists of an 

 invagination of a portion of the fore-gut into the 

 mid-gut. The mid-gut is also folded in with the 

 portion of fore- gut, so that in this region there is 



