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XXV. An Essai/ of Comparative ChcEtotaxy, or the arrange- 

 ment of characteristic bristles of Diptera. By C. R. 

 Osten-Sacken.* 



[Kead November 5th, 1884.] 



I PROPOSE the term Chaetotaxy for the arrangement of 

 bristles on the different parts of the body of the Diptera, 

 the composition of this term being analogous to phyllo- 

 taxy, the order or arrangement of the leaves of plants. 

 The characters derived from the number and position of 

 bristles (macrochfetae) have been gradually gaining 

 ground in dipterology, but it has not been attempted to 

 introduce a uniform nomenclature for them. The study 

 of the Diptera of South-E astern Asia, on which I have 

 been recently engaged, excited for the first time my more 

 immediate interest in the bristle-bearing families of Dip- 

 tera (Diptera chfetophora) they may be called), whilst my 

 attention had hitherto been confined to the Tijndidce, Taha- 

 nidce, Syrplddce, &c., which are all bristleless (I propose to 

 call them Diptera eremochseta). I soon perceived that I 

 could not proceed much further with the study of the 

 Diptera chaetophora without an attempt at a comparative 

 chsetotaxy ; and this gave occasion to the present essay. 

 In the choice of terms my principal aim was to prefer 

 such that are more or less obvious, that is, to derive the 

 names bestowed upon the macrochoBtae from the places 

 of their insertion. The bristles on the vertex, for in- 

 stance, I call vertical bristles ; those on the sides of the 

 front, fronto-orbital, &c. Such terms offer the double 



■'- The present paper appeared originally in the Mitth, d. Miinch- 

 ener Entom. Vereins, vol. v., pp. 121 — 138, 1881. In distri- 

 buting my extra copies to correspondents I added a postscript, 

 consisting of two pages printed on a separate sheet. (The contents 

 of this postscript are reproduced in an article of mine in the Wien. 

 Ent. Zeit., 1882, p. 91). In the present edition the substance of 

 the postscript is incorporated in the body of the paper ; a woodcut 

 is added (borrowed from Prof. Mik's paper, ' Zu Osten-Sacken's 

 ChiBtotaxie,' &c., in the Verb. z.-b. Ges. Wien, 1882) ; some useful 

 remarks by Prof. Mik in the same paper are adverted to, and some 

 additions are made on the last two pages. Otherwise the edition is 

 unchanged, except a few emendations of little moment. — 0. S. 



TRANS. ENT. SOC. LOND. 1884. — PART IV. (dEC.) 



