62 



The Larva of Chtronomus 



layer decreases in thickness on approaching the upper 

 bend, and is there bent into a small secondary fold which 

 projects into the stomach. It then abuts upon the 



mesenteric epithelium. The 

 passage from one epithelium 

 to the other is abrupt, without 

 transition. The muscular layer 

 is not reflected, but ends at 

 the lower bend. 



' Between the oesophageal 

 wall and its reflected con- 

 tinuation is a blood- space, 

 which does not quite reach 

 the lower bend. It has a 

 proper wall, in the form of a 

 thin membrane, and is crossed 

 by a number of oblique con- 

 nective tissue-fibres (fig. 45). 



' In the larva of Chironomus 

 (fig. 47) the layers of the wall 

 of the oesophagus, in order 

 from within, are as follows : — 

 ' I. The cMtlnous infima, 

 thrown into deep, longitudinal 

 folds ; and secreted by 



'2. The epitlieUallayei', wh.ic\i 

 is thin, and consists of a single 

 layer of cells. This kyer is 

 generally inconspicuous and 

 sometimes becomes much at- 

 tenuated, probably after it has 

 performed its function of 

 secreting the chitinous layers. 

 ' 3. The basement- memhrane is a thin and apjiarently 

 chitinous layer which lies close to the epithelium, by 



Fig. 46. — TJie same parts as in 

 fig. 45 The blood-space is now 

 contracted. 



