DIPTERA. 223 
on the front and approximated at base ; those of the Diptera 
of our first family resemble those of the Nocturnal Lepidop- 
tera in form and composition, and frequently in their appen- 
dages, but in the following and greater number of families 
they consist of but two or three joints, the last of which is 
fusiform or shaped like a lenticular or prismatic palette, fur- 
nished either with a little styliform appendage, or a thick 
hair or seta, sometimes simple and sometimes hairy. Their 
mouth is only adapted for extracting and transmitting fluids. 
When these nutritive substances are contained in particular 
vessels with permeable parietes, the appendages of the sucker 
act as lancets, pierce the envelope, and open a passage to 
the fluid, which, by their pressure, is forced to ascend the 
internal canal to the pharynx, situated at the base of the 
sucker. ‘The sheath of the latter, or the external part of the 
proboscis, merely serves to maintain the lancets in situ, and 
when they are to be employed it is bent back. ‘This sheath 
appears to represent the inferior lip of the triturating Insects 
just as the appendages of the sucker, at least in those genera 
where it is most complete, seem to be analogous to the other 
parts of the mouth, such as the labrum, mandibles, and max- 
illa(1). The base of the proboscis frequently bears two fili- 
form or clavate palpi, composed, in some, of five joints, but 
in the greater number of one or two. The wings are simply 
veined, and most frequently horizontal(2). 
The use of the halteres is not yet well known ; the Insect 
moves them very rapidly. In many species, those of the last 
families particularly, and above the halteres, are two mem- 
branous appendages resembling the valves of a shell, and con- 
nected by one of their sides, called (at/erons or cuzllerons) 
Dee ee eee 
(1) This anterior part of the head, called clypeus (my epistoma), is here repre- 
sented by that superior portion of the proboscis that precedes the sucker and 
palpi. ' 
(2) These organs, like those of the Hymenoptera, furnish good, secondary, divi- 
sional characters. Iwas the first who employed them. See the works of Fallen, 
Kirby, Meigen, Macquart, &c. 
