Regarding the Echinoderms as a whole in the light of the foregoing account, we may give the following analytic summary of the characters that distinguish them from other coelomate animals: They live in salt or brackish water; a primitive bilateral symmetry is still manifest in the right and left divisions of the coelom; the middle coelomic cavities are primitively transformed into two hydrocoels communicating with the exterior indirectly through a duct or ducts of the anterior coelom; stereom, composed of crystalline carbonate of lime, is, with few exceptions, deposited by special amoebocytes in the meshes of a mesodermal stroma, chiefly in the integument; reproductive cells are derived from the endothelium, apparently of the anterior coelom; total segmentation of the ovum produces a coeloblastula and gastrula by invagination; mesenchyme is formed in the segmentation cavity by migration of cells, chiefly from the hypoblast.
An interesting stone containing nine cavities for measures of capacity found in Pompeii and now preserved in the Naples Museum with Oscan inscriptions erased in antiquity shows that the Oscan system of measurement was modified so as to correspond more closely with the Roman, about 14 B.C., by the duoviri, who record their work in a Latin inscription (C.I.L.
Thick, with nodular segregations and abundant cavities which are often lined with zeolites.
The cells which line them and also the cavities of the tubes contain urates, which are excreted from the blood in the surrounding bodycavity.
Glessite, a nearly opaque brown resin, with numerous microscopic cavities and dusty enclosures, named from glesum, an old name for amber.
Dissepi:ments extend to the centre or axis, the ovary is divided into cavities or cells, and it may be bilocular, trilocular (fig.
The mass of cells undergoes segmentation corresponding with the outer segmentation of the embryo, and a pair of cavities - the coelomic pouches (fig.
It remains in this condition for a period of two to six weeks, and during this time the permanent organs are developed from the cells of two symmetrical cavities behind the adductor muscle.
This single cavity and its lining serve apparently for all those functions (digestion, excretion, circulation and often reproduction) which in more complex organisms are distributed among various cavities of independent and often very diverse origin.
The sexual organs - oogonia and antheridia - are borne on special portions of the thallus in cavities known as conceptacles.