70 Osten Sacken: on the atavic index-characters etc. 



requires a previous training, which every entomologist cannot be 

 expected to possess, and which would be a task worthy for an expert 

 to undertake. 



The theory of the venation of tlie Diptera has not been worked 

 out yet; so much of it as exists is nierely hypothetical. The attach- 

 ment of the wing to the thorax, and the structures connected with 

 it, deserves, it seems to me, more attention than they have received. 



The further development of chaetotaxy promises much for the 

 Classification; it may perhaps afford more atavic index es, than any 

 other set of characters. 



In my „Essay on comparative Chaetotaxy" (Trans. Ent. Soc. 

 London, 1884, p. 510 „Sternopleural bristles" and p. 512) I have 

 called attention to the two or three sternopleural bristles „the position 

 of which may afford valuable generic characters". During a visit I 

 paid several years ago to my respected friend v. d. Wulp he told 

 me that he found just these bristles very useful for the Classification 

 of Anthomyiae. And now I see in Mr. E. Girschner's paper 

 Berl. Ent, Z. XXXVIII, p. 305, that in Aricia one of these bristles 

 is inserted anteriorly (cephalad), and two posteriorly (caudad); while 

 in Lucilia and Echinomyia just the reverse takes place, two bristles 

 are situated anteriorly and one posteriorly. This, and similar cha- 

 racters so minute in appearance, may represent real indexes by means 

 of which we may discover affinities by a short cut (if I may be 

 allowed the expression), instead of a roundabout investigation. In this 

 respect Mr. Girschner's paper is füll of promise for the future. 



P.S. ad p. 71, 1. 17 from top. 

 The Dieranomyia from New Zealand (D. monilicornis O.S. 

 Studies etc. II, p. 172) has, besides the elongated proboscis, distinctly 

 moniliform antennae in the male (ordinary ones in the female) thus 

 apparently forming a passage towards Geranomyia on one side and 

 Rhipidia on the other. — In California, near S. Francisco I caught 

 a Geranomyia with almost moniliform antennae and very small fleshy 

 lobes of the forceps (1. c. p. 173). 



