562 MEDICAL ENTOMOLOGY 



very loose, and the separate tubes spread out at once when the cavity is 

 opened. The apical filament should be kept intact as long as possible, 

 to keep them together, and the oviduct sought for and cut across, so that 

 the whole ovary can be removed intact. If the ova are mature they are 

 very easily detached from their follicles, and can be removed with a pipette. 

 The alimentary tract, from the oesophagus downwards, is removed 

 by freeing it at its two ends and dissecting off the tracheae as they 



appear. The oesophagus should be cut through by 

 Dissection of the ,, . , ,. , , , 



Alimentary Tract severing the neck, and allowed to retract through 



the thorax, which it usually does readily enough ; 

 if any difficulty arises a little traction will bring it into view. The 

 anterior lobes of the mid-gut should then be reflected to one side, and the 

 whole tract dissected out from before backwards to the anus. 



The gut cannot be dissected out through the last segments, as in the 

 case of the Diptera, because the integument is far too tough to be torn 

 even if it is incised at the sides. The lateral margins internal to the 

 pleural thickening are the only places where the skin can be cut without 

 injuring the internal structures. 



The salivary glands are the most difficult of all the organs to isolate. 

 They lie in the thorax, and are closely surrounded by the large muscles 



of the legs, and are moreover deeply embedded in 

 The Salivary Glands _ b ^ J 



a mass of fat body. The tubular glands are bound 



down to the anterior end of the mid-gut, and often remain attached 

 when the head is cut off, thus rupturing the salivary ducts as well 

 as the oesophagus, in the method of dissection just described. To 

 obtain both pairs with certainty, however, a much more laborious 

 method of dissection must be resorted to. The abdomen should be 

 opened as described above, by lateral incisions, but instead of making 

 the transverse cut about the middle of the abdomen, it should be made 

 as far forward as possible. The ventral wall of the thorax should then be 

 dissected off by continuing the lateral incisions forwards, and removed in 

 pieces with the attached muscles, from the neck to the junction with the 

 abdomen. The kidney-shaped glands then come into view, and by 

 traction on the gut, which has already been exposed, the ducts leading to 

 the tubular glands can be shown up. The rest of the dissection consists 

 in freeing the structures required from the adherent fat body and the 

 specialised cells described as occurring in this region. The appearance 

 of a cleaned dissection is that of figure 1 on Plate LXX. 



For the isolation of these structures a good binocular microscope is 

 a necessity. 



