330 S. W. WILLISTON. 



scent — that family or subfamily differentiation had occurred 

 before the final reduction took place. It is also curious to ob- 

 serve that the minimum number of antennal joints in the Tipu- 

 lidae, Cecidomyidae and Chiromomidae is six, precisely the maxi- 

 mum number of the Cyclorrhapha. 



In living forms the maximum and very common number of 

 flagellar joints among the Brachycera, with the exception of 

 Rhachicerus, is eight, found so frequently in the Xylophagidae, 

 Stratiomyidse, Tabanidae and Acanthomeridae. Is this coinci- 

 dence of phylogenetic significance ? I feel quite sure that it is. 

 I think that no one can dispute the relationships between Rhachi- 

 cerus and the Xylophaginae. Is Rhachicerus a belated survival 

 of the xylophagid ancestors ? If so, the phylum must have 

 branched off long ago from the Tipulidae (the venation excludes 

 all other families, save the Rhyphidae), before the antennae had 

 become reduced below thirty segments. One thing at least seems 

 very evident, the Rhyphidae are not the nearest related to the 

 Xylophagidae of the nematocerous families, as is usually believed. 

 The Brachycera had their origin evidently directly from the an- 

 cestral Tipulidae. 



Likewise all of the five -jointed families would seem to be ex- 

 cluded from ancestral relationship with the six-jointed forms, and 

 especially the Cyclorrhapha, though possibly the reduction has 

 occurred since divergence. 



While the antennae, taken separately, may offer suggestions as 

 to phylogenies of the dipterous families, and while they may ab- 

 solutely veto such theories as imply reversion, they can settle 

 none by themselves ; they must be correlated with all the other 

 organs of the body, and must harmonize with theories derived 

 from other organs. I offer, nevertheless, the foregoing suggestions, 

 in the possibility or probability that they may find corroboration 



Secondary sexual characters are transmitted by heredity to the 

 other sex, unless inhibited by sexual utility, or, possibly, sexual 

 selection. It was for the casual statement of this law to a class 

 in paleontology that I have recently been made the victim of a 

 sensational press. The primitive eyes of diptera were doubtless 

 separated by the front equally in both sexes. As a sexual char- 

 acter the eyes have become contiguous above the antennae, 



