320 JOHN B. SMITH. 



joints, ill the latter case often long and whip like ; they are more or 

 less hairy, and are attached neat the base of the proboscis on the 

 outer side, where the maxillae coalesce with the labium. In addition 

 to the two pairs of maxillae and mandibles there is a third, unpaired 

 organ which is free, the hypopharynx. It is usually present, and 

 tube like, for the passage of saliva, the outlet l)eing near the tip on 

 the upper side ; its tip may be smooth, lance like, or hairy. Its 

 upper side is continuous with the under side of the pharynx, and the 

 whole, or in part, may coalesce with the labium below. Finally, the 

 largest, except the labium and uppermost, as well as the most im- 

 portant organ is the labrum-epipharynx, which is deeply channelled 

 on the under surface and converted into a canal by the apposition 

 of the hypopharynx below. It is through this channel that all the 

 substances used as food must pass. The two parts of which this 

 organ is composed, the labrum above and the ei)ipharynx below, are 

 sometimes separable by means of caustic potash, but are never so in 

 life. It may terminate in a single point, or in several minute ones, 

 as in the mosquito. It forms, as before stated, a covering to the 

 channel in the labium, and may be separable at the will of the in- 

 sect, as is readily seen in the mosquito when biting, or it may remain 

 tightly closed, as in the house-fly." 



The above quotation, from Dr. Williston's article in the " Standard 

 Natural History," is given as representing more clearly and defi- 

 nitely than any other, an account of the present state of our know- 

 ledge of the structure of the Dipterous mouth. Kraepelin's studies 

 have made some few modifications, but none in es.sentials, except that 

 he says there is no epipharynx, and Dr. Packard's most recent text 

 books give practically the same account. To this must be added 

 that Dr. Macloskie calls the chitinous enclosure of the muscid pro- 

 boscis, above the labellse, the operculum, and the chitinous frame 

 work at the base of the mouth system, the fulcrum. This latter he 

 considers as a modified endocranium, and the function as a sucking 

 stomach. 



As a result of my own studies, I have concluded that the mandi- 

 bles are present only in the rarest instances ; that the i)roboscis and 

 its labellate development have nothing to do with the labium, but 

 are maxillary developments ; that the labial palpi are traceable as 

 rudiments in many forms, and that neither labrum, epipharynx, nor 

 hypopharynx enter at all into the composition of the functional 

 mouth parts of the Diptera ! 



