Smilax belongs to a transition class, partaking somewhat of the nature of endogen and of exogen.

The pituitary and testes possesses a high capacity to trapping circulating D-Asp from hexogen or endogen sources.

Saponin is found in endogens and exogens.

Take the characters of exogens as distinct from endogens; even under ordinary circumstances, no absolute distinction can be drawn between them.