Oesophageal Valve 



6i 



' I. The chitinous iritima, secreted by 



' 2. Tlie epithelium. 



' 3. A muscular 

 layer, of wliich the 

 circular muscles form 

 the principal part. 



' The oesophagus is 

 contiiiuetl into the 

 cardiac chamber as 

 an inner tube, whose 

 wall becomes abruptly 

 reflected, and passes 

 upwards again, to 

 the point where the 

 epithelium of the sto- 

 mach begins. There 

 is thus an upper and 

 a lower hend in the 

 tube. The part of 

 the oesophagus which 

 is doubled into the 

 cardiac chamber is 

 called the oesopha- 

 geal valve. 



' We will now do- 

 scribe, in more detail, 

 the oesophageal valve 

 of the Simulium - 

 larva (fig. 45). In 

 the reflected wall, 

 i. e. the part between 

 the upper and Ipwer 

 bends, the layers 

 behave in the following manner : — The intima and 

 epithelium extend to the upper bend. The epithelial 



Fig. 45. — Oesophageal valve of Simiilimn-larva, 

 one-half of a longitudinal section, in, chitinous 

 intima. s.ep, stomodaeal epithelium, mj, muscle- 

 cells, b.s, blood-space, r.s.ep, reflected stomo- 

 daeal epithelium, r.m, reflected intima. p.m, 

 peritrophic membrane, tii.ep, mesenteric epi- 

 thelium. 



