B. T. LOWNE ON THE FLy's PROBOSCIS. 191 



synonym for the labrum or upper lip, will more appropriately re- 

 ceive that name, and the mouth of the insect will be understood to 

 commence at its superior extremity. 



The lower three-fourths of the conjoined pieces forming the 

 upper lip is open behind — that is towards the labium and ligula, 

 which it protects ; it is only attached to the proboscis at its upper 

 extremity, but is firmly fixed in its place in a kind of groove, 

 formed by the overlapping of the membraneous portion of the in- 

 tegument on either side of its whole length; it can be caused, 

 however, to start from its place by a little violence, without any 

 rupture of membrane, so that it projects forward and exposes the 

 cavity of the mouth. This piece is lined with epithelial cells filled 

 with orange coloured pigment. 



The salivary duct is an elastic tube, which originates in a 

 sacculus on either side of the thorax : this sacculus is extremely 

 transparent, lined with pavement epithelium, and surrounded by 

 convolutions of the salivary gland, which opens into its inferior ex- 

 tremity near the middle of the thorax. The gland itself is a very 

 long convoluted tube, which closely surrounds the sacculus, above 

 described, with numerous convolutions ; it continues, however, 

 below the sacculus in fewer convolutions, until, at the opening 

 between the thorax and abdomen, it becomes straight and passes 

 through that openmg, bound closely to the oesophagus, and then, 

 passing backwards over the pulmonary sacs, dips down below the 

 Malpighian vessels, and terminates in a blind extremity near the anus. 



This peculiar course of the salivary gland, together with the 

 close approximation of the lateral tracheae to the sacculus of the 

 gland, and the resemblance of the structure of the duct itself to 

 that of a tracheal tube, misled me, and induced me to describe the 

 relations and functions of these parts erroneously. I had not then 

 found the (rue termination of the salivary glands in coecal ex- 

 tremities, but had lost them several times, where they are closely 

 bound to the oesophagus, and where they may easily be made to 

 appear to open into it. 



Ju3t above the labium the salivary duct changes its character 

 and dilates into a cavity somewhat resembling the human glottis : 

 this is a most perfect valve, for its anterior wall is elastic and 

 pressed back at its inferior portion against the posterior wall, so 

 entirely closing the duct at this point. A pair of long slender 

 muscles, arising at the superior extremity of the fulcrum, run down 



