(47) 



STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 441 



Malpighiau tubes are described ; the function of the rectal 

 glands is believed to be of an excretory nature. 



7. As the tracheal systems of the Diptera have not received 

 much attention a detailed account of the tracheal system is 

 given. There are two thoracic spiracles, the first of which 

 supplies the whole of the head, the anterior and median 

 regions of the thorax and the three pairs of legs, and by 

 means of a pair of large abdominal air-sacs a large part of 

 the viscera. The posterior thoracic spiracle supplies the 

 muscles of the median and posterior region of the thorax, 

 especially the large dorsales muscles. There are seven pairs 

 of abdominal spiracles in the male and five pairs in the female 

 all of which are connected with tracheae only. 



8. The dorsal vessel or heart is found to consist of five in- 

 complete chambers, each with a pair of ostia. The anterior 

 end is continued forwards along the dorsal side of the ventri- 

 culus, and terminates in a glandular mass in the anterior 

 margin of the proventriculus. 



9. The reproductive organs of the male are simple, con- 

 sisting of a pair of testes, vasa deferentia, and common 

 ejaculatory duct; there are no accessory glands such as are 

 found in many other Diptera. The terminal abdominal 

 segments of the male exhibit a sinistral Asymmetry. 



The ovaries of the female, when mature, occupy the 

 greater portion of the abdominal cavity. There are a pair 

 of accessory glands (probably of a " gum " or " glue " 

 nature), three spermathecege, and a pair of vesicles used 

 during copulation. The ovipositor is about as long as the 

 abdomen, and is composed of segments six to nine. 



10. The musculature of the head is described in detail, and 

 it is found that the House-fly agrees with the blowfly in the 

 number and relations of its cephalic muscles, though in a few 

 cases the attachments are slightly different. In the haus- 

 tellum and oral lobes of the House-fly no tracheal sacs similar 

 to those described and figured by Lowne for the blowfly 

 occur, but only annulated tracheae are found, and, as these 

 are incapable of distension, the view that the oral lobes are 



