CHAPTER IV. 
NEMATOCERA. 
THE CECIDOMYID&. 
AFTER the short account of the Pulicide, we now pass on to the 
chief sections of the Diptera, and proceed to describe the more 
important families of each section, commencing with the Nematocera. 
The characters of the two sections of the sub-order Orthorrhapha, 
viz., the ematocera and the Brachycera, are as follows : 
Nematocera.* This section has the antennz composed of move than 
six joints, and the fundamental form is that of a thread. Two of the 
joints are known as the scafus, and the following those of the 
jiagellum. The third joint, that is the first flagella joint, is never so 
distinguished as to render the succeeding joints accessories to it, 
the joints being formed in such a way that we cannot consider the 
flagellum as one joint, marked by annulations. 
Palpi composed of four or five joirits. 
Brachycera. Antenne short, three-jointed. The two joints of the 
scapus likewise separated. Third joint remarkably developed and 
has a peculiar anatomical structure, which is most probably for 
sensorial functions. The succeeding joints absent, or very few in 
number ; when present they are in the form of a bristle. In some 
genera the first joint of the flagellum is not enlarged, then the follow- 
ing joints are more numerous, and most seem to be sensorial in 
function. These joints are so closely approximated that they can 
almost be considered as one joint, marked by annulations. The 
palpi are 1 to 2 jointed. 
Although the above characters seem to sharply separate these two 
sections, they nevertheless are so closely connected by intermediate 
types, that some cannot be satisfactorily placed in either division. 
The Xylophagide,; for instance, can be placed on the limits between 
both sections, and amongst the Nematocera the Riyphide are bess, 
related to the Brachycera. 
* Vide p. 18. + Vide p. 20. 
