Note 21 — Chapter III · COCKROACHES; EARWIGS; THE GREAT GREEN GRASSHOPPER; THE WATER SCORPION; THE WATER BOATMAN; CORIXA.
Reading edition
This refers to the gizzard. Echinus was used to denote the third stomach of Ruminants (now called the manyplies), because it was thought to resemble a hedgehog rolled up.