CHAPTER IV. 



NEMATOCERA. 

 THE CECIDOMYID.^. 



After the short account of the PulicidLe^ we now pass on to the 

 chief sections of the Diptera, and proceed to describe the more 

 important famiUes of each section, commencing with the Nematocera. 

 The characters of the two sections of the sub-order OrtJiorrhapha, 

 viz., the Nematocera and the Brachycera, are as follows : 



Nematocera* This section has the antennae composed of more than 

 six joints, and the fundamental form is that of a thread. Two of the 

 joints are known as the scapns, and the following those of the 

 flagellum. 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 joints. 



Brachycera. Antennas 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 i 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 Xylophagidm,\ for instance, can be placed on the limits between 

 both sections, and amongst the Nematocera the Rhyphidcf. are nearly 

 related to the Brachycera. 



* Vide p. 18. t Vide p. 20. 



