326 S. W. WILLISTON. 



take into account all vestiges and aborted organs if one would 

 arrive at precise results. The Phoridae, for instance, have been 

 shown by Brues and others to possess two scape joints, though 

 but one has usually been ascribed to them. And this will prob- 

 ably be found to be true of all the other so-called two-jointed 

 antennae, such' as those of certain cyrtids, empidids and doli- 

 chopodids, under close examination. I have arranged the families 

 in the following list not quite in the supposed order of their re- 

 lationships, in order to bring out more clearly the antennal struc- 

 ture. I have also for the few families showing archaic forms 

 given the extremes in parenthesis, with the " normal " or usual 

 numbers in the regular column. 



Tipulidae (6-39) 12-16 Acanthomeridae 10 



Cecidomyidae(6-36) ... 12-16 Tabanidae 6-1 



Psychodidae 12-16 Leptinae 3-8 



Mycetophilidae 12-16 Nemestrinidae 5-6 



Pachyneurinae 12-16 Mydaidae . . . '. 4-5 



Rhyphidae 12-16 Apioceridae 3-5 



Dixidae 15 Asilidae 3-5 



Culicidae 14— 1 5 Therevidae 3-5 



Blepharoceridae 9—1 5 Scenopinidae 3 



Chiromomidae 6-1 5 Bombyliidae 3-5 



Orphnephilidae 1 1-12 Dolichopodidae 4-5 



Bibioninae 8-12 Empididae 3-5 



Scatopsinae 9- 10 Lonchopteridae 6 



Simuliidae 10 Phoridae 6 



Xylophaginae (13-30). 9-10 Cyclorrhapha 5-6 



Stratiomyidae 7- 10 



In this list we are at once struck with the predominance of five 

 groups having the maximum normal number of sixteen, fifteen, 

 ten, six and five. And I venture to suggest that these five groups 

 represent, in the main, long since divergent phyla of diptera. 

 Not invariably of course, because coincidences may and often do 

 occur in the different lines of descent. There are quite a num- 

 ber, it is seen, having the maximum number of fifteen. Possibly 

 these may represent one common branch from the sixteen-jointed 

 antennae, possibly several. But, in none of these groups, unless 

 it be the fifteen jointed, and of course the primitive Tipulidae and 



