Note k — BOOK IX.
Reading edition
As I have shew’d before, that the Bodies of Birds are nicely pois’d to swim in the Air; so are those of Fishes for the Water, every Part of the Body being duly balanc’d, and the Center of Gravity, (as I said in Note (f)), accurately fix’d. And to prevent Vacillation, some of the Fins serve, particularly those of the Belly; as Borelli prov’d by cutting off the Belly-fins, which caus’d the Fish to reel to the right and left Hand, and render’d it unable to stand steadily in an upright Posture.