Note 2239 — BOOK IX. THE NATURAL HISTORY OF FISHES.

Cuvier remarks, on this passage, that the mollusca have, instead of blood, a kind of azure or colourless liquid. He observes also, that insects respire by means of tracheæ, or elastic tubes, which penetrate into every part of the body; and that the gills of fish are as essentially an organ of respiration as the lungs. All, he says, that Pliny adds as to the introduction of air into water, is equally conformable to truth; and that it is by means of the air mingled with the water, or of the atmosphere which they inhale at the surface, that fishes respire.