Section 20. Finally, We Note Two Series of Buds of Cells, One on Either

side of the archenteron in Figure 7 ii. In 8 these buds have become hollow vesicles, growing out from it, the coelomic pouches. They are further developed in 9; and in 9 ii., which is a diagrammatic figure, they are indicated by dotted lines. They finally appear to (? entirely) obliterate the segmentation cavity-- they certainly do so throughout the body; and their cavities are in time cut off from the mesenteron, by the gradual constriction of their openings. In this way the coelom (body cavity) arises as a series of hollow "archenteric" outgrowths, and ms. becomes the alimentary canal. mt.c., the metapleural canals, probably arise subsequently to, and independently of, the general coelomic space, by a splitting in the body-wall substance.