Later the ciliated ring or velum disappears and seven imbricated calcareous plates, made up of flattened spicules, are formed on the dorsal surface.
Here the medusoid, attached by the centre of its ex-umbral surface, has lost its velum and sub-umbral muscles, its sense organs and mouth, though still retaining rudimentary tentacles.
It is seen from the foregoing account of medusa - budding that the entocodon is a very important constituent of the bud, furnishing some of the most essential portions of the medusa; its cavity becomes the subumbral cavity, and its lining furnishes the ectodermal epithelium of the manubrium and of the sub-umbral cavity as far as the edge of the velum.
The manubrium bearing the gonads is mouthless, and the umbrella is without tentacles, sense-organs, velum or radial canals.
The communication with the atrium is guarded by a valvula cardiaca dextra, which only in function represents the mammalian tricuspid; it consists of an oblique reduplication of the muscular fibres together with the endocardiac lining of the right ventricle, while the opposite wall is convex and forms neither a velum nor papillary muscles, nor chordae tendineae.