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 4 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 ruge when the proboscis is retracted. The 
duct is very extensile. 
Near the distal extremity of the rostrum (Pl. VI., s v) 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 two 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. 
