Abstract
Weak oxytocic activity can be extracted from the neural complexes of two solitary ascidians, Chelyosoma productum and Pvura haustor. This activity does not resemble neurohypophysial oxytocin pharmacologically or chemically. It can also be found in tissues other than the neural complex. Pyura extracts exert a weak antidiuretic effect but Chelyosoma extracts do not. The similarity of ascidian neural complex activities to those of the vertebrate neurohypophysis are considered too superficial to support the argument for homology of these organs.