102 GNATS OR MOSQUITOES — CHAPTER VI 



specimen, and place it on a slide with a little salt solution, 

 and carei'uUy remove the legs and wings. Next tear open 

 the thorax, so as to loosen the anterior attachment of the 

 tube, and then carefully partially detach the last two abdo- 

 minal segments by separating the delicate intersegmental 

 membrane. Now place one needle so as to fix the last two 

 segments, and with the other entangled in the thorax pull 

 steadily on the anterior portion, when the alimentary canal 

 and its appendages will be drawn out intact attached to the 

 hinder fragment. If the operation be successful even the 

 oesophagus and salivary glands may be included in the pre- 

 paration, but as a rule, the tube is torn just behind the 

 latter, so that they and the so-called aspiratory vesicle are 

 left behind. 



Assuming, however, that, as is usually the case, only a 

 portion of the oesophagus is brought away, we find that, 

 immediately after entering the abdomen the digestive canal 

 expands into the chylific ventricle or stomach, which forms 

 by far the largest part of the intestinal canal. It is of con- 

 siderable width throughout, but especially so at its hinder 

 •end. Throughout its entire length it is thrown into deep 

 transverse folds, which recall somewhat the valviila conni- 

 ventes of the higher animals, and probably serve the same 

 purpose of increasing the secretory area. In insects that 

 have but recently emerged from the pupal stage some 

 remnants of the last meal of the larva may occasionally 

 be seen, but in the well-established imago plant juice, 

 pollen, or blood will alone be found. Lastl}^ succeeding 

 the broad, hinder part of the stomach, comes the hind gut, 

 and running into the junction of the two are seen opening 

 five long, convoluted, dark-tinted glandular bodies, the Mal- 

 phigian tubes. These are supposed to have an excretory 

 function, and as uric acid and other renal products have 

 been found in them, the balance of opinion regards thom 

 as renal organs. They are lined with a series of large 

 nucleated cells, the protoplasm of which is exceptionally 

 rich in pigment and granules. These cells are arranged 

 in a somewhat peculiar fashion, for as they are too large 

 to admit of their forming a complete lining, the cell of one 



