39 
"secundum principia Naturae et Artis", and states in an- 
other place that "classis ac ordo" are the work "Natu- 
rae et Artis". Both of the writers, however, were per- 
fectly convinced that some definite system was an in- 
dispensable requisite, a "filum ariadneum - sine 
quo chaos", and to both of them belongs the honour 
of having, each in his own department of science, estab- 
lished that essential system. 
The three remaining parts of ARTEDI'S "Ichthyologia" 
constitute, as LINNAEUS remarks in the Introduction, the 
practical application of the theories put forward in 
what preceded. The first of them is entitled "Genera 
Piscium", and contains a presentment of the System of 
Fishes as it was conceived by ARTEDI. The Class of 
Fishes he divided into 5 Orders, one of which, however, 
the "Plagiuri (with horizontal caudal fin)", embraced 
the whales. Though ARTEDI on several occasions pointed 
out that whales in many particulars resembled Mam- 
mals, he did not seem able, any more than his pre- 
decessors, to decide upon excluding them from the class 
of Fishes. It was not until LINISLEUS published the tenth 
edition of his "Systema Naturae", 20 years later, that 
they were once for all banished from the Class to which 
they have no just claim to belong. The other four Or- 
ders in ARTEDI'S System are: Malacopterygii, the soft- 
rayed fishes, Acanthopterygii, the spiny-rayed osseous 
fishes, Branchiostegii, osseous fishes but lacking bones 
in the gills, and Chondropterygii, real cartilaginous fishes, 
embracing also sturgeons and lampreys. This classifi- 
cation is marred by numerous shortcomings, as was 
only to be expected considering it was a first attempt. 
When sturgeons and lampreys, however, are removed 
from the last-named Order, the Chondropterygians form 
a unitary conception, and they still go under the same 
name to this day. The Branchiostegals, on the other 
hand, formed an entirely artificial group, and were soon 
disintegrated as such, the several members being rele- 
gated to other places in later Systems. The remaining 
two, again, the Acanthopterygians and the Malacoptery- 
