B. T, LOWNE ON THE PROBOSCIS OP THE FLY. 129 



Tho abdominal crops are strongly muscular, and it is from 

 these that the copious saliva is poured with which the insect 

 moistens its food. The position of these crops is a marvellous 

 instance of adaptation, for the fly's head is exceedingly heavy 

 from the size of its eyes and optic ganglia, as well as from the 

 number of muscles moving the proboscis, so we find the abdo- 

 minal stomachs balancing the weight of the head by acting as a 

 counterpoise behind the wings. 



By examining the labium it will be found that its superior ex- 

 tremity is prolonged, behind the joint of the proboscis, to about 

 half a line above the lower extremity of the fulcrum as a flexible 

 tube, which widens out at its upper part, so as to represent in some 

 degree the form of the human glottis and trachea. A large 

 tracheal tube, marked with a stronger spiral than any other 

 in the tracheal system of the head or thorax of the blow fly, ter- 

 minates in it, and if this be traced back, it will be seen to traverse 

 the head, and entering the thorax, to divide into two branches, 

 each portion passing outward into a sacculus, communicating with 

 the main lateral tracheal system of the insect. 



I may here remark that the tubes fonning the tracheal system of 

 the abdomen, differ from those of the head and thorax very con- 

 siderably, not only in general arrangement, but also in the much 

 greater distinctness of the rings with which they are marked. 



The air tube which surmounts the labium, opens upon its an- 

 terior surface, near the middle of that organ ; the air so conducted 

 through it passes to the triangular opening between the lips of the 

 proboscis, in a tube (labial tube), bounded behind and laterally by 

 the labium and labial palpi, and anteriorily, partly by membrane 

 and partly by the oesophageal tube, which opens into it just above 

 the triangular aperture. 



The lips of the proboscis, when at rest, are closely applied to 

 each other ; their outer surface is rough and covered by numerous 

 long curved hairs, but their inner surface is smooth and soft, 

 covered with a yellow pigment, which washes away in water a short 

 time after the death of the fly ; these inner surfaces exhibit the so- 

 called false tracheal tubes. 



When the organ is treated with liquor potassse and afterwards 

 mounted in balsam, the false tracheae appear to he imperfect on their 

 cutaneous surface, having a dentated margin ; as far as the chitin- 

 ous element is concerned this is really the case, and in the lips of 



