124 PREDACIOUS AND PARASITIC 



absorbed by them would pass, and which in time would convey it 

 to the anterior extremity of the hollow shown at a, which consti- 

 tutes the floor of the mouth. In this hollow, when at rest, lie the 

 long lanceolate tongue (Hgula), b, and the horny upper lip, c^ both 

 of which are partly shown more highly magnified at Fig. 2. When 

 these parts are in place, the upper lip, c, constitutes, with the 

 bottom of the groove or hollow, «, a tubular passage, through 

 which fluids, absorbed by the lobes, find their way to the pharynx 

 and thence to the oesophagus. This passage presents ample space 

 for the passage of pollen-grains also ; but a comparison of the 

 diameter of those found in the oesophagus with the width of the 

 " pseudo-tracheae " of the lobes at once makes it evident that it is 

 not by their means that the pollen-grains reach the mouth. 



An examination of the upper lip, as shown at Fig. 2, suggests 

 an explanation of the manner in which the ingestion takes place, 

 which is doubtless correct. The upper part of the extreme end is 

 divided into teeth, which are sufficiently wide apart to admit of 

 pollen passing between them; but between these are smaller 

 brush-like processes, which appear especially fitted to sweep 

 it from the flowers upon which the fly feeds into the cavity of the 

 mouth, where it is met by the secretion issuing from the duct, 

 which proceeds from the salivary glands, and which terminates in 

 the tongue. This duct is shown on Fig. i, at j". 



The uniformity with which the pollen-grains are to be found in 

 all parts of the alimentary system, and their great abundance in 

 the sucking stomach, indicate pretty clearly the important share 

 they take in nutrition. To assure myself more fully of this, I have 

 experimented by supplying the flies, both reared and captured, 

 with saccharine foods. The flies were kept under the most natu- 

 ral conditions consistent with confinement. They at first attacked 

 the food with avidity, but although fresh leaves, etc., were given 

 daily they soon became languid and generally died about the fifth 

 or sixth day. On examination of a fly under these conditions, the 

 sucking stomach is invariably found full of a clear syrupy fluid, 

 while the proper stomach and intestines appear collapsed and 

 empty. It seems probable that, as in the human stomach, the 

 presence of more or less solids is an important factor in stimulat- 

 ing the digestive organs into action. Possibly, the effect of the 



