498 C. E. Osten-Sacken's essay on 



advantage of being easily remembered, and not easily 

 disputed; many of them have been anticipated by earlier 

 writers. In following this plan, however, I met with a 

 difficulty in the incomplete or uncertain terminology* of 

 certain parts of the body of the Diptera, especially of the 

 thorax, and this afforded me an opportunity for de- 

 veloping it. In doing this I purposely preferred a 

 purely conventional to a homological or anatomical 

 nomenclature. The latter is much easier to praise than 

 to carry out, being often subject to uncertainty and 

 dispute. Thus, what dipterologists hitherto called meta- 

 notum has been recently proved to belong to the meso- 

 thorax (see the paper of Mr. Hammond in the Journal 

 Linn. Soc, vol. xv.), and if the arrangement is sustained 

 we shall have either to change the term for another or 

 to continue to use it as a merely conventional term. 

 The difficulties of descriptive Entomology are great 

 enough without such uncertainty of terms, and it is 

 evident that a conventional terminology offers more 

 chances of fixity ; it may very well exist alongside of a 

 homological and anatomical terminology. It was princi- 

 pally the pleura which required some development of the 

 nomenclature of its different regions, and of the sutures 

 which divide them. The term pleura itself, being con- 

 ventional, and not anatomical, I have formed the new 

 names of the combinations of this word with other 

 words indicative of the position of the parts which I 

 intended to name (mesopleura, metapleura, &c.). 



Bristles easily fall off, and the scars which they leave 

 are not always recognisable ; in such cases we may 

 sometimes be in doubt whether we have a defective 

 specimen or an individual aberration before us. State- 

 ments about chaetotaxy must therefore be made, as well 

 as received, with some caution. 



It is hardly necessary to add that in this, as in all my 

 previous publications, I adopt Loew's terminology (ex- 

 plained in the Monogr. N. Am. Dipt., vol. i.) as my rule 

 and the basis to start from, only I prefer the Latin terms 

 to their equivalents in English. Although somewhat 

 incomplete and too hastily written, that chapter was 

 composed by Loew at a late period of his career, and 



- I deliberately prefer terminology, which is consecrated by usage 

 and by the best writers, to horisinology, which is not to be found in 

 Webster's Dictionary, except in the incorrect form of orismology. 



