406 THE ALIMENTARY CANAL OF THE IMAGO. 



sericteria of the larva. Each consists of a single long con- 

 voluted tube, which commences in a blind extremity near the 

 posterior end of the abdomen. The gland tube is wavy rather 

 than convoluted in the abdomen, but forms a long coil in the 

 thorax, which lies externally to and in relation with 'the chyle 

 stomach. If uncoiled, the gland tube would probably exceed 

 6 cm. (2 inches) in length ; it consists of a basement membrane, 

 lined by a single layer of beautiful rodded cubical epithelial 

 cells, 20 to 25 p, in diameter. The gland tube measures from 

 0.2 to 0.3 mm. in diameter. 



In Lucilia it terminates in a cylindrical reservoir, from which 

 the duct arises, but in Calliphora the gland tube opens directly 

 into the salivary duct ; this converges towards its fellow, with 

 which it unites before passing through the cervical region to 

 form the common lingual duct. 



The ducts of the lingual glands and the common lingual 

 duct are exceedingly elastic, and consist of a peritoneal 

 membrane, lined by a cuticular intima, which exhibits a spiral 

 fibre similar to that of a cylindrical tracheal vessel. The 

 external coat of the lingual duct is very thick, yellow in colour, 

 and thrown into rugai when the proboscis is retracted. The 

 duct is very extensile. 



Near the distal extremity of the rostrum (PL VI., s i 1 ) the 

 common duct changes its character. It loses its spiral fibre 

 and its extensibility. It becomes transparent, and dilates into 

 a cavity shaped somewhat like a larynx. This cavity is closed 

 by a very perfect valve, formed by its anterior wall, which is 

 elastic and pressed in towards the posterior wall of the cavity. 

 The indented portion receives the insertion of t\vo long 

 slender muscles, which arise from the proximal extremity of 

 the fulcrum ; their action is to render the tube patent and thus 

 permit the escape of the saliva, which Kraepelin says is jetted 

 out by the intra-thoracic pressure. Beyond the valve the 

 lingual duct is a chitinous tube, which enters the base of 

 the hollow ligula through which the salivary fluid flows ; the 

 orifice of the duct is at the apex of the ligula. 



