EXTERNAL ANATOMY. 21 



claimed thirty -nine in a particular genus of CECIDOMTID^E (Cero- 

 zodia), but this has been disputed on the grounds that some of 

 the joints are merely annular impressions. Rhachicerus (LEPTIDJE) 

 has twenty-eight joints, and some genera of CECIDOMYLDJB possess 

 this number also. 



The antennae in the BBACHYCEEA consist technically of only 

 three joints, but in some genera (Hexatoma, in TABASTDJE, Xylo- 

 <phagns and Khachicerus in LEPTJD.E) the 3rd joint is either dis- 

 tinctly or apparently divided into several joints, so that at first 

 sight it is not easy for a beginner to distinguish the location of a 

 species by the antennae alone. But in all such cases the very 

 short palpi and .the totally different scheme of venation afford a 

 certain clue to their identity. 



In the NBMATOCEKA the two basal joints are almost invariably 

 differentiated from the rest, and are known as the scape or scapug, 

 the remaining joints being called iheflagellum. The scape nearly 

 always bears a few stiff bristles, either irregularly placed, or 

 arranged in one or two more or less distinct rows near the apical 

 margins ; it is sometimes bare or practically so, but never verti- 

 cillate. The flagellum in most of the TIPULID-ZE and in some 

 other groups, bears a whorl of fine hairs symmetrically arranged 

 (in the TIPUUD^E a very common number is four, two above and 

 two below, the upper ones often the longer) around each joint, 

 and the antennae are then spoken of as verticillate. This is the 

 normal form of antenna in the TIPULID.E. A few genera in that 

 family have pectinate antennae in the male, that of the female 

 being verticillate or much less conspicuously pectinate. The 

 CHIBOXOMLIXE and CULICID^; normally possess excessively plumose 

 antennae in the males, those of the females being generally verti- 

 cillate, whilst CECIDOMYID.! generally possess verticillate antennae 

 in both sexes. 



In the CYCLOBKHAPHA only three joints are present, of which 

 the first is always short, often extremely so, the third frequently 

 being annulated, or possessed of a number of finely impressed 

 lines giving the appearance of a number of joints closely annealed. 

 It is curious that in these latter cases the 3rd joint never possesses 

 more than seven such annular impressions, thus suggesting eight 

 annealed joints, because the nematocerous antennse most likely to 

 be confused with such a form are those like Bibio, Plecia, etc., in 

 which the flagellum generally consists of eight subequal homologous 

 joints (though perfectly distinct from one another), whilst the 

 two basal or scapal joints have some considerable resemblance 

 to the first two joints of the antenna in Xylophagus. It is this 

 latter form, which is by no means infrequent, that may be mis- 

 taken by the beginner for an eight-jointed nematocerous antenna. 

 However, in all such doubtful cases the structure of the palpi 

 and the distinctly different venation immediately decide the 

 question of af&nity. 



With the Cyclorrhaphic antenna we have little to do in this 

 volume, but it may be stated that although it consists of three 



