The ectoderm furnishes the general epithelial covering of the body, and the muscular tissue, nervous system and sense-organs.
The nematocysts of the ectoderm may be grouped to form batteries on the tentacles, umbrellar margin and oral lappets.
There is some evidence that in this group the ectoderm of the oesophagus is chiefly concerned with digestion, whereas the endoderm of the intestine is limited to the absorption of the soluble products.
A considerable part of the alimentary canal is said to be derived from the ectoderm in the buds of both Cephalodiscus and Rhabdopleura.
- Portion;of the body-wall of Hydra, showing ectoderm cells above, separated by " structureless lamella " from three flagellate endoderm cells below.