B. T. LOWNE ON THE PROBOSCIS OF THE FLY. 127 



maxillary palpi, the remainder of the proboscis lying within the 

 cavity so produced. 



When the proboscis is at rest or retracted, the maxillary 

 palpi lie close to the margin of the oral cleft, directed forwards, 

 but when it is fully exserted, they are turned upward in contact 

 with its integument. As they are not apparently supplied with 

 any muscles, and from their position during exsertion of the 

 proboscis, appear as if turned out of the way of injury, this 

 would indicate that their fmiction is called into activity during the 

 period when they lie along the margin of the oral cleft, so that it 

 seems probable they assist the insect in its search for food ; in fact^ 

 their position is the same as that of these organs in the Lepidoptera, 

 excej^t when the proboscis is exserted. 



The second joint of the proboscis encloses two tubes ; the an- 

 terior of which forms the termination of the oesophagus, and con- 

 sists of parts homologous to the epiglottis and mandibles. This 

 tube is connected with the fulcrum by the membranous oesophagus, 

 and fonns an elbow-like joint protected from pressure behind by a 

 small semi-circular chitinous piece homologous to the mentum, or 

 accessory to it, if the larger portion which I have named the fulcrum 

 be considered as the homologue of that part. 



The mandibles are further connected with the basal part of the 

 proboscis by a pair of levers, nearly a line in length, flattened out 

 at their upper extremity for the insertion of powerful muscles, and 

 strongly suggestive of the elongated tendons by which the mandi- 

 bles of insects are usually moved. Their action appears to be to 

 move the oesophageal tube, raising it slightly from the labium 

 against which it lies ; as well as to assist in folding the proboscis. 



The posterior tube is homologous to the labium and labial palpi ; 

 it is complete above, but open in front below, partially enclosing 

 the oesophageal tube. It terminates in a triangular opening 

 between the lips of the proboscis, which are supported upon its 

 margin. In the embryonic or pupa state, this tube is represented 

 by three distinct rods, clearly homologues of the labium and labial 

 palpi, the second and third joints of the palpi being represented 

 by the margin of the triangular opening, so that the lips them- 

 selves may be considered appendages of the labial palpi. 



Behind the labium are the terminal lobes of the maxillfe ; in the 

 young state these may be seen to be composed of two layers, an 

 inner membranous layer, largely supplied with air tubes, and an 



