28 DIPTERA OF AUSTRALIA, 



them, more particularly as the terminologies of any two authors 

 are unfortunately only rarely alike. Throup'hout the following 

 work I shall adhei'e to the terms adopted by Baron Osten- 

 Sacken and Prof. H. Loew in their masterly monogra|)hs of the 

 Diptera of North America, regarding it, in the words of the latter, 

 as the " duty of a later author to accommodate himself to the 

 usages of his i)redecessoi'S, especially those who have written 

 standard works," that is, as far as it lies in his power. The 

 following, then, is for the most part taken from the first volume 

 of those monographs, hy Prof. Loew. 



1. The Head. 



The back of the head opposite to the thorax is the occiput, and 

 is pi'ominently perceptible in both Diptera and Hymenoptera 

 carrying their heads free ; that portion of it lying over the 

 attachment of the head is the nape {cervix). The front, forehead, 

 or brow (frons) is that part of the head stretching from the 

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

 compound eyes. The crown (vertex) is the upper part of the 

 head, upon which frequently are the simple eyes {ocelli), generally 

 three in numbei'. The limit between the occiput and the front 

 is styled the vertical margin (margo verticalis ). Most of those 

 Diptera undergoing their metamorphoses within the larva-skin 

 possess, immediately above the antennae, an arcuated impressed 

 line, which seems to separate from the front a small, usually cx'es- 

 cent-shaped, piece, termed the frontal crescent (hinula frontalis) ; 

 the impressed line, which continues over the face nearly as far 

 as the border of the mouth, is called the frontal fissure (Jissura 

 frontalis). When the eyes meet on the front so as to divide it 

 into two triangles, the superior one is called the vertical triangle 

 {trianyulum verticale), the inferior the frontal triangle (triangu- 

 lumfrontale). The anterior portion of the head reaching from 

 the antennae to the border of the mouth or oral margin (peris- 

 toinium) is the face (fades). The antennae are separated 

 into two series of joints ; the first, consisting of the two 

 ■basal joints, called the joints of the scapus, and the following 



