The first are irregular and arenaceous masses, which pile themselves upon plants and solid bodies immerged in fresh water. Such are the _spongilles_, upon which anatomic and embryonic observations have very frequently been made in relation to the group more immediately under consideration. The second is found in almost every sea; especially are they found in the Mediterranean, the Red Sea, and the Mexican Gulf. Affecting warm and quiet waters, they attach themselves to bold and rugged rocks at depths ranging from five to twenty-five fathoms. They are erect, pendent, or spreading, according to their form or position. Fig. 10, drawn from Nature, represents a very remarkable form of sponge, which was fished up in sixty fathoms. The sponge is very common in the Mediterranean and round the Grecian Archipelago, and is known vulgarly under the name of the Marine Mushroom, the Sailor's Nest, and the fine soft sponge of Syria. It is a mass more or less rounded, covered with a mucous bed, glutinous above, formed of a light elastic but resisting tissue full of gaps, and riddled with air-cells. This tissue is formed of delicate flexible fibres, uniting in all directions by anastomosis, but presenting numerous pores, which are formed by what is termed osculation, having irregular _conduits_ which connect them. In this tissue certain very small solid bodies are discovered, named _spiculæ_. The _spiculæ_ are siliceous or calcareous in their nature, varying according to the species, and sometimes varying even in the same species. Some of these resemble needles, others are pin-like, and others again resemble very small stars. [Illustration: Fig. 10. Spongia, half the natural size, attached to its rocky bed.] The physiological function of those tubes and orifices which present themselves on all parts of the sponge has been interpreted in various ways. Ellis, writing in 1765, supposes that they were the orifices of the cells occupied by the polypi. In 1816, Lamarck still advocated this opinion; and even now we find the observer, whose notes M. Frédol has edited with so much judgment, asserting that "the inhabitants of the sponge are a species of fleeting, transparent, gelatinous tube, susceptible of extension and contraction; young polypes, as we may call them, without consistence, without cilia; incipient polypes, in short, of very simple but sufficient organization. The animalcule of the sponge is a stomach, without arms, very simple, very elementary--in short, an animal all stomach!"