Ectoderm [noun]

The terms ectoderm and entoderm were introduced by Allman in 1853 for the two cell-layers in the Hydrozoa.

Ontogeny teaches unmistakably that its elementary organs, the epidermic cells, develop entirely from the ectoderm.

Amongst other structures which arise from the important layer of ectoderm are the teeth.

The skin corresponds with the ectoderm of Hydra, although it is a vastly more complicated affair.

In the typical invertebrate eye, on the contrary, the retinal cells are differentiated from the external ectoderm.

Later, in front of the primitive streak, a thickened band of ectoderm appears, broadening out posteriorly.

But perhaps the most remarkable of all is the list of structures which take their origin from the ectoderm of the embryo (see A).

The first part to appear is a portion of the inner ear, which shows itself as a round, hollowing of the ectoderm.

In yet others it is partly derived from endoderm and partly from ectoderm (primitive streak of amniotic Vertebrates).

It is also sometimes formed from ectoderm, as in the Vertebrata at the nerve crest and other places.