Have you ever wondered about the origin of the use of the terms Ectoderm and Endoderm for the two epithelial layers of the hydra polyp? They were coined by George James Allman in a monograph he published in 1871. The citation for the monograph is:

George James Allman (1871). A Monograph of the Gymnoblastic or Tubularian Hydroids. The Ray Society, London.

The monograph contains a Glossology of terms applicable to hydroids. Ectoderm and Endoderm are defined as follows:

Ectoderm (ecto = outside, derm = skin) – The more external of the two organized layers of which the body of every hydroid is composed.

Endoderm (endo = within, derm = skin) – The more internal of the two organized layers of which the body of every hydroid is composed.

I inherited a copy of the Monograph from Dick Campbell. This copy was originally held by the Geological Society of London.