W. H. HARRIS ON THE DENTITION OF THE DIPTERA. 391 



attention to the dental oi'gans, and watched the actions of the 

 living insects while partaking of food, my faith in the absolute 

 correctness of the statement has been shaken. That these 

 channels are capable of conveying liquids goes without saying, 

 but I am sceptical as to this being the only, or even primary, use 

 for which these organs were designed. I can recommend this 

 subject as a special study to any one in search of employment, 

 fully believing that there is much to be learned respecting these, 

 so-called, suctorial channels. 



It is impossible, within the limits of this paper, to do more 

 than glance at some of the leading features of the subject ; 

 accordingly a few examples of typical groups of teeth have 

 been selected for description and illustration. Before, however, 

 proceeding to their consideration I may be permitted to make 

 a few preliminary remarks of a general character. 



The dental organs of flies are arranged in two nearly, if not 

 absolutely, symmetrical groups, occupying a somewhat central 

 position near the median line of the lobes of the proboscis. 

 Each lobe contains one group of teeth. The groups of teeth 

 may consist of one, two, three, or four distinct rows of organs, 

 which, for convenience of description, may be divided into two 

 distinct sections. Those mouths which have the organs ar- 

 ranged in two single symmetrical rows may be referred to as 

 simple, while those which have two or more such rows in each 

 lobe may be termed compound. When the rows of teeth 

 are thus duplicated, they form compact and somewhat complex 

 groups. 



By far the larger number of species of flies possess their dental 

 organs arranged on the compound system ; but although this is 

 the case, it must not be hastily assumed that they present a 

 monotonous similarity. Many slight changes occur which the 

 practised eye soon detects, and which relieve them from this 

 accusation ; for instance, the number of individual teeth in each 

 row may vary considerably : they may be long or short, slender 

 or robust ; they may be of uniform breadth throughout their 

 entire length, or they may be broad at the base with narrow 

 free ends, or these latter distinctions may be exactly reversed. 

 Then again the free ends of the teeth are subject to variation of 

 form : they may be bi- or tridentate. Some of the teeth may 

 bear from one to four small denticles between the large lateral 



