On the Ultimate Structure of Marine Sponges. XXXI.-On the Ultimate Structure of Marine Sponges. By H. J. CARTE, F.R.S. &c. THE " ultimate structure" of the marine is, mutatis mutandis, the sanie as the "ultimate structure" of the freshwater Sponges. In July 1857 I described and illustrated the " Ultimate Structure of Spongilla," (Annals, vol. xx. p. 21, pl. 1). In January 1859 I expressed doubt as to the position of the cilia in the " ampullaceous sac," and my conviction that they were external instead of internai, contrary to my first statement (ib. vol. iii. p. 12). In October 1861 I again returned to my ori-ginal view, viz. that the cilia were inside (ib. vol. viii. p. 290). This discrepancy I can now adjust; for, the cilium of the sponge-cell being retractile and the sponge-cell itself amoeboid and free to change its position in situ, the cilia may at one time be put forth outside, and at another inside the ampulla-ceous sac, the latter probably being their normal position. Now what is this " anpullaceous sac"? for although it is twelve years since my description of it was published (viz. 1857), no one, to my knowledge, has referred to it but Pro-fessor H. James-Clark, of Boston, in June 1866 (Mem. Boston Soc. Nat. Hist. vol. i. pt. 3, p. 1, 1867), a fact which may be excusable to those who have been brought up in a language different from that in which it was published. "Ampullaceous sac" is the term which I applied to certain groups of unciliated and monociliated sponge-cells or monad-like bodies which are tessellated together in a globular form, and scattered plentifully here and there throughout the sponge so as to make up the greater part of its bulk. The globular form presents a circular opening or transparent area through which the cilia may be observed to play internally; and when the young Spongilla is grown from the seed-like body, and a solution of carmine is put into the water around it, these glo-bular bodies alone become coloured; that is to say, they alone take in the carmine; and thus their globular form becomes clearly defined and differentiated from the rest of the mass. Hence the little globular bodies are clearly the animal ex-pression of the sponge in particular, as they are respectivelythe only mouths and stomachs of the sponge-in short, thenutritive apparatus, ail the rest being subsidiary. When the Spongilla thus fed with carmine is torn to pieces,the monad-like bodies (which we shal henceforth call" sponge-cells ") of which the ampullaceous sac is composed are foundto have taken in the carmine, while the absence of the cilium329
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