Hydra cross section
A cross section through a hydra (Phylum Cnidaria, class Hydrozoa) showing the mid-section of the animal. Visible are the epidermis (outer layer of cells), the gastrodermis (the inner layer of red cells), and the mesoglea (the thin line dividing the two). The opening in the center is the gastrovascular cavity. Seen at ~200x magnification.
Copyright © 2011 Marc Perkins