31 
tudo quorundam Piscium ad speciem diversorum, qui 
in situ Partium externarum semper, numero plerumque, 
Figura et Proportione saepe conveniunt." The genera 
are recognisable by certain characters, which are of 
such a nature that, by their aid, "the various fishes 
belonging to different genera can be told apart and be 
referred to their respective genera". 
As ARTEDI, both here and in several other places 
in his writings, makes a point of the universal appli- 
cability of the general statements which he enunciates 
regarding Fishes, with which he is directly concerned, 
we are justified in looking upon his reform w r ork as of 
the utmost import for the whole systematics of Zoology. 
For instance, he remarks, with reference to genus-cha- 
racters, that natural characters constitute "primum et 
prsecipuum Fundamentum non solum Ichthyologies sed 
totius reliquse Historise naturalis", and similar extracts 
might be multiplied. 
With regard to the characters to be made use of 
in delimiting the various genera, ARTEDI points out how 
essential it is that they should be chosen judiciously, 
for otherwise the classification will be of no practical 
use from a scientific point of view; thus, the general out- 
ward appearance is apt to be seriously misleading, as 
the example of the tench and the lake-trout plainly 
proves, for though they resemble one another fairly 
closely in external shape of body, yet one of them be- 
longs to the carp-genus and the other to the salmon- 
genus. He also calls attention to the fact that the same 
characters may have different systematic values in dif- 
ferent groups, and that as a consequence it will not by 
any means always be feasible to employ the same kind 
of characters as distinguishing marks for congeners in 
different orders; he illustrates his argument by adducing 
examples. 
The next question taken up for discussion is which 
properties of fishes lend themselves for employment as 
genus-characters, and which do not. ARTEDI considers 
that the best and most constant genus-character for os- 
