206 [February, 



wedge " has been inserted, for it was only quite recently that " milli- 

 metres " were used at all, excepting in quotations. 



Carrying my analysis outside the entomological publications of 

 this country, I scarcely find (excepting in some issued in the British 

 Colonies) any system of measurement employed other than by milli- 

 metres. 



The old descriptive authors (commencing with Linne) did not, as 

 a rule, think it necessary to indicate any dimensions other than com- 

 parative, thus arguing that their readers should possess at least as 

 much knowledge as they. Later, a system of measurement by "inches" 

 and "lines " was instituted, and outside this country this was usually 

 based upon the "Paris inch" (cf. Burmeister's "Manual," English 

 translation, p. 26), but not universally, for there were "inches " other 

 than Parisian (excluding our own). The "Paris inch" (which was 

 divided into 12 "lines," as is our own) equalled about l|th English 

 (i. e., about 1 inch, lj lines), and, occasionally, the "Paris inch" and 

 decimals were employed. Until quite recently (as already demon- 

 strated), English authors used the English inch and lines (or fractions) 

 exclusively. When we consider that the old " Paris inch " equalled 

 about 28 millimetres, and that the English inch measures slightly over 

 25 millimetres, it is easy to imagine that much confusion and error re- 

 sulted from this employment of a term which had such a strikiDg 

 discrepancy in its possible interpretation according to the nationality 

 of the describer. This discrepancy may appear small to the general 

 travelling public whose ideas have been " enlarged " when trying to 

 equalize an English and German " mile," but it seriously affects en- 

 tomologists who occupy themselves with the study of minute insects, 

 or of the comparative lengths of the parts of an insect. The use of 

 the English " inch " is liable to more than double the chance of error 

 than if millimetres had been employed to give effect to the author's 

 meaning. (Occasionally, authors have used centimetres and milli- 

 metres, or fractions of a centimetre, the latter course being especially 

 objectionable). 



Measurement by lines (whether " Parisian " or English) fails in 

 minute insects. It is not, therefore, necessary to enlarge on the 

 custom universal with investigators of minute forms of animal (or 

 vegetable) life, to whom the microscope (with powerful objectives) 

 and micrometer are absolute necessities ; these use the decimal 

 system ; no other would avail. With these it is often necessary to 

 carry the decimal system to extreme minuteness ; for all practical 

 purposes in entomological descriptions (concerning external anatomy 

 only) the millimetre (with large fractions) is sufficient. 



