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An essay of comparative Ühaetotaxy, 
or the arrangement of characteristic bristles of Diptera, 
by Q, R. Osten-Sacken. 
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 phullotaxy, the order or arrangement of the 
leaves of plants, The characters derived from the number and posi- 
tion of bristles /macrochaetae), 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 Eastern Asia, on which I have 
been recently engaged, exeited for the first time my more immediate 
interest in the bristle-bearing families of diptera /Diptera chaetophora 
they may be called), whilst my attention had hitherto been confined 
to the Tipulidae, Tabanidae, Syrphidae ete., which are all bristleless 
(I propose to call them Diptera eremochaeta). 1 soon perceived that 
I could not proceed much further with the study of the Diptera 
chaetophora, without an attempt at a comparative chaetotaxy; and this 
gave occasion to the present essay. 
In the choise of terms, my prineipal aim was to prefer such 
that are more or less obvious, that is, to derive the names, bestowed 
upon the »macrochaetae from the places of their insertion. 'The bristles 
on the vertex, for instance, I call vertical bristles; those on the 
sides of the front, ‚fronto-orbital etc, Such terms offer the double 
advantage of being easily remembered and not easily disputed; many 
of them have been antieipated by earlier writers. In following this 
plan however, I met with a diffieulty in the incomplete or uncertain 
