262 THE AMERICAN MONTHLY [Sept 



show the teeth, a denial of their existence would be re- 

 ceived, probably coupled with an assurance that there 

 were no teeth, but some minute hairs on the edge of the 

 labella which had been mistaken for them. It is a curi- 

 osity of microscopy that often,unless it is known what to 

 look for, it is quite possible to miss seeing a structure or 

 detail, from the fact that its focus is at a different dis- 

 tance from some near, yet more prominent object. This 

 is precisely the reason, coupled with the fact, that the pro- 

 boscis is usually looked at with low powers, why these es- 

 cape observers ; they lie at the base of the false or pseudo 

 tracheae, at a different focus, and the chitine of which they 

 are composed being a light yellow and transparent, they 

 are easily overlooked. 



The teeth show between eleven of the false tracheae, and 

 six appear to be double, making a total of sixteen on each 

 labellum. With the exception of one at the end furthest 

 from the head, they have a cleft edge, thus securing two 

 points to each tooth, and, one might suppose from this, 

 are used for pricking or gently scraping a surface, possi- 

 bly with the object of accelerating a flow of liquid. They 

 are much thinner than those of the Scatophaga, and not 

 round and tooth-like, but riband-like in appearance. The 

 bases appear slightly rounded, and from these the teeth 

 broaden and taper to a very thin edge — they might be 

 compared to a row of chisels with cleft edges. 



To see them a magnification of three hundred and fifty 

 diameters is quite sufficient — a good quarter-inch power 

 would do ; the field at the back of the teeth is rather ob- 

 scured by the chitinous support of the labellum, but if 

 the bases of the false tracheae are focussed,the character- 

 istic edge of a tooth is probably seen, and that once 

 found, the rest is easy. The length of the row of teeth 

 is three two-hundredths of an inch. — Knowledge. 



