72 
LECTURE VIII. 
common Carp it is supposed to arrive at the age 
of two hundred years. 
We have now passed through all the Linncean 
orders of Fishes, but there still remains a large 
tribe which I before mentioned under the title of 
Cartilaginous Fishes. I also observed that they 
differ from all other fishes in having a compara- 
tively soft or cartilaginous skeleton, and that some 
particularities in the structure of their gills in- 
duced Linnasus improperly to rank them as an 
order of the Amphibia under the name of Na?ites, 
Of the Cartilaginous Fishes the first genus is 
that of Petroinyzon or Lamprey. The character 
is a long, round. Eel-shaped body; a mouth fur- 
nished with numerous teeth in circular rows, and 
seven round spiracles or breathing-holes on each 
side the neck: these breathing-holes each lead into 
a tubular cavity, lined with a red pleated mem- 
brane, thus forming a series of organs analogous 
to gills in fishes, but not quite of a similar struc- 
ture, and more approaching to that of lungs. 
The common or great Lamprey is an inhabitant 
of the sea, but comes into rivers during the spring. 
It is viviparous like the Eel, which it resembles in 
