DISSECTION OF LARGE NEMATOCERA 421 



gradually, to allow the natural peristalsis of the muscular wall to thrust 

 the contents down to their proper place. 



If the ovaries are mature, and if they are not required for examination, 

 some at least of the mature ova should be released through a slit in the 

 wall, to make more room to work. 



The salivary glands of the small Nematocera are a little difficult to 

 dissect, as even with a dissecting microscope of moderate powers one 

 cannot see them very clearly. They lie in the anterior 

 and ventral part of the thorax, below the main mass Dissection of the 

 of muscle, and are obtained by drawing them through 

 the neck. The following method is that usually employed, and the one 

 recommended for the examination of the glands of mosquitoes. Place 

 the specimen, freed from its appendages and vestiture as before, on 

 its side with the proboscis towards you. Steady the thorax with a 

 needle held in the left hand, and place another needle, held in the right 

 hand, behind the head. Then make a series of short and gentle pulls, 

 drawing the head towards you and into the drop of saline. If this 

 is done gently and carefully the integument of the neck and the muscle 

 fibres attaching it to the thorax will rupture, while the duct of the 

 salivary glands remains intact, and is pulled out of the neck and thorax 

 with the glands still attached. The delicate oesophagus ruptures and 

 retracts into the thorax ; the pair of cervical tracheae (see page 68) 

 often require to be cut with a needle. When the head is free it will 

 be found that it has attached to it a small mass of whitish tissue, which 

 consists of some fat body, muscle fibres, a part of the main nerve trunk, 

 and the glands. The mass should be freed from the head by a sharp 

 cut with a lancet-like needle, and moved gently in the saline. The 

 glands can usually be easily differentiated from the other tissues by 

 their glistening appearance, and may be isolated, though this is not 

 usually necessary in routine examinations. 



If the salivary glands and the alimentary tract are required from the 

 same specimen, the salivary glands should be dissected out first. The 

 oesophagus ruptures when the head is pulled away, and retracts 

 into the thorax. 



The dissection of the Larger Nematocera, such as the Tabanidae, 

 is carried out in the same way. It is better, however, to use a paraffin 



trough rather than a slide, on account of the large size 



r -ru r i A t *u T u -j The Tabanidae 



of the organs. The salivary glands or the Tabanidae 



extend into the anterior end of the abdomen, and cannot be extracted 

 by the anterior route with the same certainty. If both glands are 



