THE existence of the nests of corallines and lithophyta, and the mechanism of their polypi, made me conjecture, that it was the same with respect to sponges; that animals, nested in the interstices of their fibres, gave them their origin and growth: but I had not yet seen nor discovered the insects, nor observed their work. Sponges appeared to me only as skeletons: but I at length discovered these worms, which form sponges, in the four following species: 1. _Spongia Americana tubo similis_; The tube-like sponge of Plumier. 2. _Spongia Americana longissima funiculo similis_; The cord-like sponge of Plumier. 3. _Spongia Americana capitata et digitata_; The fingered sponge of Plumier. 4. _Spongia Americana favo similis_; The honeycomb sponge of Plumier. These four kinds only differ in form: they have the same qualities, are made by the same kinds of worm, and what may be said of the one agrees exactly with all the rest; for I made the same observations upon them all. They may be classed among the _spongiæ hyrcinæ_, so called by J. Bauhin, because of the roughness of their fibres, by a metaphor, from pieces covered with mud; or among those called by Pliny _tragos_, or _aphysiæ_, being foul, and difficult to cleanse; and may take the name, which Father Plumier has given them, drawn from their figure. These four kinds of sponges are composed of hard, firm, dirty fibres, sometimes brittle; separated one from another, having large hollows, or cylindrical tubes, dispersed thro’ their substance. These tubes are smooth within. The interstices of their fibres are filled with a mucilaginous gluey matter, when the sponge is just taken out of the sea. The mucilage is of a blackish colour, soon putrifies in the water, or falls into dust when dried in the sun. When a fresh sponge is squeezed, this mucilage comes out frothy, by the mixture of the windings of its fibres: it always issues forth with sand, or little parcels of shells crushed by the sea. These fibres, which consist of the twisted doubles of the sponge, form as it were a labyrinth filled with worms, which are easily crushed, and their juice is confused with the mucilage; but having carefully torn the sponges, and their gross fibres, I discovered the living worms, such as I shall mention hereafter. These species of sponge commonly grow upon sandy bottoms. At their origins we perceive, as it were, a nodule of sand, or other matter, almost petrified, round which the worms begin to work, and round which they retire, as to their last seat or refuge; where I had the pleasure of seeing them play, exercise themselves, and retire, by examining them with the microscope; and I have even made my observations without its assistance. _A Description of the Worms which form the Sponges._