In different parts of the coelenteron the endoderm may be of three principal types - (i) digestive endoderm, the primitive type, with cells of large size and considerably vacuolated, found in the hydranth; some of these cells may become special glandular cells, without flagella or contractile processes; (2) circulatory endoderm, without vacuoles and without basal contractile processes, found in the hydrorhiza and hydrocaulus; (3) supporting endoderm (fig.   anvd [Please select]

, on the other by possessing a central cavity (the coelenteron or "hollow inside") the walls of which are the walls of the body and consist of _two_ layers of cells separated by a structureless, or apparently structureless, jelly.   anvd [Please select]