440 Osten Sacken: on (he charaders of the three dhnsions of 



The alula, and the axilhiry cxcision iicar it, arc cithcr little 

 dcveloped, or rudimentary, or entirely absent. In Culex, Chironomtis^ 

 Tanypus they are nioderately devcloped; in Ceratopogon rudimentary 

 or entirely absent. Their entire absence is espccially noticeablc in 

 the Tipulidae Avhere, owing to the usually sniall posterior angle of 

 the wing, the interval between the last longitudinal vein and the 

 niargin is very narrow, sometimes a niere narrow strip, without any 

 vestige of an axillary excision or an alula; the antitegula is neverthcless 

 ahvays present. The Mycetophilidae and Cecidomyidae show no 

 trace of an alula or an excision ; only Ceroplatus and some Sciophilae 

 have rudiments of them. — All these characters have been very little 

 noticed in the existing descriptions. 



All degrees of the development of the venation are found aniong 

 the Netnocera vera, from the complete venation of the Tipididae 

 with seven longitudinal veins and a discal cell, to the degraded ve- 

 nation of Heteropeza and Miastor, which has but two longitudinal 

 veins. 



The so-called ambient vein is well-marked in the Tipulidae, 

 Ctdicidae and Psychodidae (also in Dixa); it is weak or altogethcr 

 wanting in the Chironomidae, Mycetophilidae and Cecidomyidae. 

 The contrast between stout veins near the anterior niargin, and the 

 evanescent ones of the remainder of the wing is strongly mai'ked in 

 the CMronomidae only; in this respect this faniily resenibles the 

 genera Bibio, Simidium and Scatojyse among the Neynocera ano- 

 mala. 



The theory of the venation of the Diptera is not advanced enough 

 to enable us to formulate a general character common to the Nemo- 

 cera vera, and distinguishing their venation from that of the Nemo- 

 cera anomcda. Such a character may be in existence, but it has 

 not been discovered yet. 



The Netnocera vera in their imago-state are never prcdaceous. 

 that is they never bunt for other insects, and it is probably for this 

 reason that their faces and eyes never show the broad surface in 

 front, which distiguishes the predaceous tribes [Asilidae, Dolicho- 

 podidae, Empidae), and their legs are not formed for seizing the 

 prey. But there are some genera of Nemocera, which draw blood, 

 and possess an apparatus for that purpose, while their next relatives 

 are harmless. Thus we have as blood-suckers Culex and Anopheles 

 (Culicidae), some species of Ceratopogon (Chironomidao) and Phleho- 

 tomus (^Psychodidae). As a rule the female alone is a bloodsucker 

 and has for this purpose mouth-organs of a peculiar structure, diffe- 

 ring from those of the male (comparc Dimmock, Anat. of the moutli- 



