NORTH AMERICAN DIPTERA. 319 



A CJOUVTRIBl TIOI^ TOWARD A KSfOWLEDOE OF THE 

 MOUTH PARTS OF THE DIPTERA. 



BY PROF. JOHN B. SMITH. 



" The mouth parts of Diptera are wholly suctorial, and differ from 

 those of the Lepidoptera in that all the component parts may be 

 brought into use. They differ not a little, however, in different flies, 

 as might be supposed from their diverse habits. In some they are 

 adapted for piercing animal or vegetable substances, and are, in con- 

 sequence, firmer and more slender ; in others, and by far the greater 

 number, they are adapted only for sucking up juices or such sub- 

 stances as may be dissolved by means of their saliva. Grains of 

 j)ollen have been observed in the digestive organs of the Syrphid?e, 

 and other flower flies, but, as a rule, fluids alone serve as food. Many 

 have the proboscis wholly retractile into the oral cavity, and fur- 

 nished with one, or even two hinges, by which, when at rest, it may 

 be folded up. In others the proboscis is not retractile, and 'either 

 projects in front, or backwards under the abdomen. AVhile it is 

 usually short, it may be as long or longer than the body. Finally, 

 a few species have the mouth parts rudimentary, and take no nour- 

 ishment in the adult stage. 



"The different parts consist of the labium, the maxillae, maxillary 

 palpi, mandibles, hypopharynx and labrum-epipharynx, a term used 

 by Dim mock, to whom our clearest knowledge of the mouth parts 

 of Diptera is due. The labial palpi are thought to be wholly want- 

 ing. The labium is always present, more or less fleshy, and provided 

 with muscles, and is grooved or channelled upon the upper side to 

 receive the other parts in a sheath completed by the labruni. At its 

 tips there is a pair of joints called the labellae. In the mosquito 

 these are small, where they serve simply to guide the piercing portion 

 between them, the labium itself being bent backward beneath the 

 thorax in its middle. Very often they are large and more fleshy, 

 and on the inner sides have a roughened surface composed of the 

 pseudo-trachea, which, as in the house-fly, serve as a means of attri- 

 tion. The maxillie and mandibles are frequently absent, the latter 

 most often ; when present they are slender and bristle like. The 

 maxillary palpi are always present, and consist of from one to five 



