442 ZV. droits so neat’s Account of 
fhort from any one part to another, would anfwer the fame 
purpofe ; but if you take the terms of the meafures, and 
compare them one with another, or all of them to a Angle 
one, a method may be deduced for determining the fpecies, and 
defcribing each with accuracy, and that is the method which 
I ufed. 
There is no doubt that fi flies have a regular growth, and that 
all their parts have a proportional increafe : it is therefore of 
no confequence whether the meafure be taken from an old 
or a young fubjeft, it will be always of the fame ufe for 
determining the fpecies. The term to which I refer all the 
reft, is taken from the diftance between the apex of the 
upper jaw, and the bafis of the fin of the tail. The extremity 
of the upper jaw is the point from which I take the dif- 
tance to all the other parts. To determine w 7 ith more accuracy 
the junftion of the fin to the tail, I incline the fin fo as to 
form an angle with the tail ; 1 take the diftances with a pair of 
compafles, to avoid the irregularities of the furface of the body, 
which are infinitely various. When I have taken the diftance 
with the compafles, I make a reference to a rule, which is 
divided in Englifli inches, each of them fub-divided in tenths. 
To exemplify my practice in a fifti of the fuppofed length of 
40 lines from the upper jaw to the tail, and from the fame 
point to the anus of 20 lines, I fay, that the diftance from the 
head to the tail compared with the diftance from the head to 
the anus is in this fpecies as 40 to 20, which I exprefs in 
this manner: Lc. : A :: 40 : 20, which I thus reduce, 
Lc. : A :: 10 : 5. I then take the length from the upper ja\v 
to the beginning of the dorfal * fin, and to its end : next from 
* I meafure the dorfal and anal fins at their bafis, never in their margin. 
the 
