lOO Larval and Pupal Stages of Bibio Johaiiiiis L. 



smaller diameter (Text-fig. 9). The oesophagus ultimately joins the 

 cardia or first portion of the mesenteron, at the end of the first seg- 

 ment. 



The Salivary Glands. The salivary glands are rather small, and lie 

 one on either side of the alimentary canal, towards the end of the first 

 segment. Each gland is hollow and has a lining of protoplasm. Strands 

 of protoplasm also stretch across the interior of the gland forming a 

 complicated network in which, as well as in the lining of the gland, are 

 large nuclei. The salivary duct passes forwards ventrally from the 

 anterior end of each gland. 



The oesophagus is continued a short distance into the cardia, and is 

 then sharply turned back and passes upwards again to the point where 

 the epithelium of the cardia begins, forming an oesophageal valve. The 

 part of the oesophagus forming the valve is very similar in structure to 

 that of other parts as far as the first bend. It consists of intima, 

 epithelium, and well-developed circular muscle fibres. The part of the 

 oesophagus between the two bends is composed of an epithelium of much 

 larger cells than the other part, without the muscle fibres. The space 

 between these two parts forms a blood sinus, and is crossed by bands of 

 connective tissue fibres, and there are also bands of longitudinal muscle 

 fibres between the two portions of the oesophagus. 



The part of the cardia which follows the oesophagus, and surrounds 

 the valve, consists of deeply staining columnar cells, followed by less 

 deeply staining cells, and this tissue makes several folds into the cardia. 

 These folds chiefly involve the epithelium, but also the moderately 

 developed coat of circular muscle fibres to a small extent. From the 

 anterior part of the cardia a number of bands of muscle fibres stretch to 

 the walls of the oesophagus, without resting on the alimentary canal 

 throughout their length. 



From the cardia the three large caeca take origin ; the longest, which 

 lies parallel to i^e mesenteron and ventral to it, is about 2-5 mm. long. 

 The other two, which are of about equal length (1-3 to 1-4 mm.), open 

 laterally from the cardia and are slightly inclined upwards. 



The caeca are composed of an epithelium similar to that of the 

 mesenteron, the cells of which are rather larger and project slightly 

 into the lumen. Outside the epithelium is a membrane of connective 

 tissue, but no muscle fibres. The caeca are filled with a finely granular 

 substance. 



The Stomach which follows the cardia has walls of the following 

 structure, from within outwards: 



