378 KANSAS UNIVERSITY SCIENCE BULLETIN. 



The Heart. This is shown in fig. 2 h., pi. XLIII. It lies along 

 the dorsal wall of the abdomen till near the thorax, where it 

 dips ventrally to a position just above the alimentary canal 

 and extends forward, passing through a cellular mass above 

 the region of the oesophagial valve and on into the head.* 



The Fat. Body. The fat body often occupies a considerable 

 portion of the abdomen and is made up of many lobes. Figure 

 9 shows the fat bodies of a female fly after being fixed in 

 alcohol for a time (ventral view) . 



The Nervous System. The nervous system is less specialized 

 than in many other Diptera. The three thoracic ganglia are 

 large while the five ganglia of the abdomen are comparatively 

 small, the last two being close together and the terminal one 

 larger than the others. (For general position and relative size 

 see Fig. 6, PI. XLIV.) 



THE RESPIRATORY SYSTEM. 

 The respiratory system (Fig. 5, PI. XLIV) consists of two 

 longitudinal trunks running from the head to the posterior 

 end of the abdomen. These are connected in the thorax by a 

 large commissure, and in the head by a small one. The head 

 and thorax are well supplied with large tracheal branches 

 while the abdomen possesses a great network of tiny thread- 

 like tubes arising from the rather small tracheal trunks. 

 These little tubes ramify to all parts of the abdomen, bind- 

 ing together the loosely joined ova of the female, interlacing 

 the many loops and folds of the Malpighian tubes and tying 

 the fat body with all to the digestive canal. Thus we find in 

 the abdomen on either side a longitudinal tracheal trunk, 

 and throughout a mat of slender tracheal filaments. These 

 tracheal trunks are not straight tubes, but curved at the six 

 points where the branches leading to the abdominal spiracles 

 are given oft', namely, at the points between the second and 

 third, third and fourth, fourth and fifth, in the fifth and in the 

 sixth segments ; the spiracular openings being located on the 

 lateral surface of the body as follows: first one in the second 

 segment near the junction of second and third, second one in 

 third near the junction of second and third, third one in middle 

 of segment 4, fourth one near the middle of segment 5, fifth 

 one near the middle of segment 6, sixth one in seventh seg- 

 ment near its union with segment 6. These spiracles show up 



* Goi'don Hewett states that the dorsnl vpkspI of the horse fly tei'minafes in a mass of 

 cells on dorsal side of ventriculus, 



