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THE GUIDE TO NATURE. 



what may be called half-tubes. This 

 may be seen in Fig. i, where the two 

 edges of the split tube are defined by 

 what appears to be a saw-tooth margin, 

 a delicate arrangement that the micro- 

 scope explains. 



Flies with these soft tips to their 

 tongues live, for the most part, on li- 

 quid food, although they do get a part 

 of their nourishment from solid ma- 

 terials that they scrape with their 

 teeth, for a fly has teeth, carrying them 

 at the base of the tongue, some owning 

 three rows, broad and flat, and each 

 with its free margin cut into one or 

 more sharp, saw-like points. 



The tip of the tongue (Fig 2) has 

 two parts or lobes separated by a clear 

 space. At the rear of this space, on 

 both sides between the split tubes 

 there are. as the photograph shows, six 

 teeth. In Fig. 1 the teeth are visible 

 in three rows on each side but of a 

 different form. It is with these that 

 the fly scrapes the solid food which it 

 eats. The surface of some harci ob- 

 jects, such as loaf sugar, hard cake, 

 even varnished wood, sometimes shows 

 parallel scratches made by flies' teeth. 



The fly's food must be very finely 

 pulverized, or preferably in solution, 

 so that it may pass through the split 



FIG. 3. PART OF DRONE FLY'S TONGUE. 



tubes and onward to the stomach. To 

 soften the hard food, the fly exudes a 

 great flood of saliva through the half- 

 tubes of the tongue, dissolves the sur- 

 face of the sugar or other substance, 

 or scrapes it with the teeth when the 

 saliva is withdrawn, carrying with it 

 the sugar or the minute particles. 



That flies, disturbed fiom the dishes 

 on our own tables, may leave drops 

 of their saliva for us to swallow is not 

 a pleasing thought, but it is true. We 

 are just beginning to learn that they 

 are dirty creatures, and that the filth 

 which they may carry from one place 

 to another may become a source of 

 danger to us or even of death. But 

 this need not detract from the inter- 

 est in the structure of these tongues, 

 which are an admirable bit of Nature's 

 handiwork. 



FIG. 2. TONGUE OF HOUSE FLY. 



MAKING PHOTOMICROGRAPHS. 



The Guide to Nature has extensive 

 facilities for making photographs of 

 microscopic objects. This can be done 

 even from temporary mountings, if the 

 specimen is sent in good condition. 



Correspondence solicited regarding 

 work in special investigations. 



