In this communication, the author described some observations made by him in the autumn of 1845, by which he had ascertained that in the Common Green Polype, as had previously been observed in the Hydra fusca, generation takes place at the approach of winter by the development of impregnated ova.

Professor Thomson ascertained, that, at this season, while a number of the polypes bore the spermatic capsules near the base of the arms, a few animals were to seen, on which, besides these capsules, an ovum was developed from the exterior of the middle of the body.