Xll ON THE TERMINOLOGY OF DIPTERA. 



put (occiput)] that region of it lying over the junction of the head 

 is the nape (cervix). The part of the head which reaches from 

 the antennae as far as the occiput and is limited laterally by the 

 compound eyes, is the front (frons), the^pper part of which is the 

 crown (vertex), the limit between the front and the occiput having 

 the name of vertical margin (margo verticalis). The middle of 

 the front being often of a more membranaceous substance and 

 sometimes differing io color from its borders, is called the frontal 

 stripe (vitta frontalis). On the crown, there are the simple eyes 

 (ocelli}, being usually three in number and forming a triangle, 

 sometimes on a sharply defined triangular space, the ocellar trian- 

 gle (triangulum ocellare). Most of those Diptera which undergo 

 their metamorphosis within the larva-skin possess, immediately 

 above the antennas, an arcuated impressed line, which seems to 

 separate from the front a small piece usually of the form of a cres- 

 cent, the frontal crescent (lunula frontalis). The impressed line 

 itself, which continues over the face nearly as far as the border of the 

 mouth, is called the frontal fissure (fissur a frontalis). It owes its 

 origin to a large bladder-like expansion which exists at this place in 

 immature imagos, and which helps them in bursting the pupa case. 

 The frontal fissure of course is the true anterior limit of the front, 

 and the frontal crescent in fact belongs to the face ; however, on 

 account of its usual situation, it is commonly considered as a part 

 of the front. In many genera the eyes of the males meet on the 

 front, so as to divide it into two triangles, the superior of which is 

 called the vertical triangle (triangulum verticale), the inferior the 

 anterior frontal triangle (triangulum frontale anterius), or simply 

 the frontal triangle (triangulum frontale). The anterior portion 

 of the head reaching from the antennas to the border of the mouth 

 or oral margin (peristomium) is called the face (fades). In most 

 Diptera it is divided into three parts adjoining each other, the 

 limits of which depend on the situation which the frontal fissure, 

 continued to the oral margin occupies in the developed imago ; 

 the form and mutual proportion in size of these parts are of the 

 highest value in the classification and distinction of the species of 

 Diptera. Beneath the antennae there are in many Diptera longi- 

 tudinal holes for their reception, the antennal furrows (fovece an- 

 tennales) ; the antennas lie in them while the insect is still in the 

 pupa case, sometimes even after its exclusion. That part of the 

 head which lies on the side beneath the eyes is the cheek (gena). 



