DIPTERA OF MINNESOTA. 



29 



over the entire body. Three of these spiracles show on the thorax 

 in Fig. 4. It will be seen, therefore, that one could hold a flly's 

 head under water indefinitely without drowning it, but if all these 

 breathing" holes or spiracles are closed the insect dies. In order to 

 make the anatomical details more clearly understood we give a 

 dorsal view, Fig. 5 of Glossina, taken from Austen's "Monograph 

 of the Tse-tse Flies." 



A few words on the internal anatomy of a fly may not be out 

 of place. The mouth parts have already been referred to. In the 

 figure of the House Fly, page 24, only the lower end of the labium 



Fig. 9a. The labella of a 

 house fly, greatly enlarged, 

 showing rasp-like surface, 

 used in scraping or tearing 

 delicate surfaces. 



Fig. 10. Two types of the 

 last tarsal joint. Each 

 shows pulvilli. The 

 left figure has the em- 

 podium bristle like; the 

 figure on the right has 

 the empodium pulvilli- 

 form. 



shows, the so-called proboscis. The end of this proboscis, the 

 labella, is practically the food-obtaining organ. It is covered by 

 many tiny horny ridges (see Fig. 9a), with which solid food may 

 be rasped, and the fine particles obtained by this rasping, mixed 

 with and dissolved in a salivary secretion, are sucked into the 

 mouth, and thence find their way into the oesophagus. A glance 

 at Fig. 12 will give the reader a very good idea of the alimentary 

 canal of a fly. Calliphora erythroccphala ; oe, is the oesophagus con- 

 nected with the crop, cr, and through the proventriculus, pv, with 

 the chyle stomach, ch. This latter passes into the proximal intes- 

 tine shown in a coil, and this, through the distal portion of the in- 

 testine, di, connects with the rectum. The tracheae supplying 

 these organs with oxygen are marked tr in the drawing; trs — the 

 tracheal sacs ; mm represent the malpighian tubules, which, upon 



