CLASSIFICATION OF DIPTFRA. 29 



to the invagination of the head-capsule within the thorax. 

 The invaginated portion of the head-capsule is deeply cleft 

 both on its dorsal and ventral surface. In other Nematocera 

 and many Tabanidae this condition is still more marked, and 

 the head-capsule is reduced to the form of diverging chitinous 

 rods in relation with the pharynx (Fig. g). These are termed 

 ' Zopfgraten ' by Brauer.* I shall speak of such rods as the 

 cephalo-pharyngeal apophyses ; they apparently represent the 

 inflections which form the endo-cranial skeleton in more per- 

 fectly developed head-capsules, and afford a key to the 

 morphology of the so-called pharyngeal skeleton of the 

 acephalous larvas. 



The division of the order into orthoraphic and cycloraphic 

 sub -orders was first suggested by Brauer [12], and is un- 

 doubtedly morphologically correct ; it has not, however, the 

 advantage of being of ready application ; first, because every 

 variety of transition exists between the lowest orthoraphic 

 and the highest cycloraphic forms ; and, secondly, because 

 in many cases the developmental history of a species is un- 

 known. Hence systematic entomologists need a more artificial 

 division founded upon characters which are externally manifest 

 in the imago. The Diptera are therefore generally divided 

 into the four following sub-orders : Aphaniptera, Nematocera, 

 Brachycera, and Pupipara. 



These sub-orders are not, however, of equal import. The 



Nematocera are a fairly natural group, but the Brachycera 



consist of at least two distinct sub-divisions of the Diptera. 



The Aphaniptera are nearly related to the Nematocera, and 



are a semi-parasitic and probably degraded group, formerly 



classed with the Hemiptera. The Pupipara, on the other hand, 



are related to the higher forms of Brachycera, but are also 



parasitic insects, exhibiting very remarkable modifications 



both in their development and structure. 



The Aphaniptera, or fleas, although almost apterous, having- only scale- 

 like rudiments of wings, present so many points of affinity with the Diptera 

 that they are included in the order by most modern systematists. 



* Consult Brauer's [14] figures of the head of Limnophila, Pcccilostola, 

 Dolichopus, Tabanus, etc. 



