W. H. HARRIS OX THE DENTITION OF THE DIPTERA. 



393 



concentrated carbolic acid to immerse the lobes. At first the 

 object will appear clouded and indistinct, but as the acid pene- 

 trates it will become beautifully transparent, and the dissection 

 may be completed in the liquid. 



In order to do this make three clean cuts in the direction of 

 the lines indicated in the accompanying figure. Separate the 

 uppermost membrane, w^liich contains the object sought, from 

 the one resting on the glass slip, which may now be discarded, 

 and with a fine hair brush free the object from all internal 

 organs, and finally mount in Canada balsam. It will be found 

 that a small quantity of the acid is miscible with the balsam 

 without decreasing the transparency of the latter, and that, for 



hard parts of insects, no better or more expeditious method could 

 be desired. 



We will now proceed to consider a few typical examples of the 

 teeth of flies : — 



Figures I and 2, Plate 19, represent moieties of the dental 

 organs of the Blow-fly, Calliophora erythrocephcda^ and Polietes 

 lardaria respectively, both typical of the compound group. The 

 teeth comprising the primary set in the first-named species may 

 be described as bidentate rods, having a U-shaped section for 

 about two-thirds of their length ; the remaining third becomes 

 flattened and solid at the free end. There are usually ten or 

 eleven such organs in each half of the mouth. Each organ of 

 the secondary set of teeth arises from two plates at the base 

 of the pseudo-tracheae. With a graceful curve the two parts 

 of each tooth approach each other, and at a short distance from 



