Paper, 'On the flask-shaped ectoderm and spongoblasts in one of the Keratosa' by George Bidder Bidder writes: 'In my “Note on Excretion in Sponges,” [see PP/19/16] published by the Society in the ‘Proceedings’ of this year, I said: “Both from my own ob­servations on an Aplysilla (?) . . . . and from a study of Schulze’s detailed description .... particularly in I am persuaded that the ectoderm cells of the horny sponges are of the same form and character as those in the Homocoela.”' Annotations in pencil and ink. Includes three plates of magnified anatomical figures. Subject: Zoology Received 15 June 1892. Read 16 June 1892. Communicated by Adam Sedgwick. A version of this paper was published in volume 52 of the Proceedings of the Royal Society as 'On the flask-shaped ectoderm and spongoblasts in one of the Keratosa'. 1892