The arrangement of this internal system of vascular lamellæ is simple. What they amount to is a certain definite number of linear adhesions between the two walls of an originally undivided gastro-vascular space, by which that space is divided up into a central stomach and a peripheral portion, and the peripheral portion thus further divided into the four stomach pockets. Perhaps the idea may be conveyed by likening the whole medusa to a couple of bowls fitting closely one within another and plastered together at the margins. The exumbrella then would correspond to the outer bowl, the subumbrella to the smaller inner bowl, and the original undivided gastro-vascular space to the space between the two. If now the walls of the space be cemented together in four horizontal curved lines just in the plane where the bottoms are bending round to become the sides of the bowls, leaving four interspaces between the ends of the lines, we should have the original space divided into a central horizontal somewhat lens-shaped region between the bottoms of the two bowls that would correspond to the central stomach, and a peripheral vertical portion between the sides of the bowls that would correspond to the peripheral gastro-vascular system; central and peripheral portions would communicate by the four interspaces between the lines of fusion, which would correspond to the four gastric ostia. If, further, the vertical peripheral portion be subdivided by four more lines of fusion running vertically at equal distances apart, each connecting above with the middle point of the corresponding horizontal line of fusion, we should have the simple peripheral portion divided into four parts, corresponding to the stomach pockets, by four vertical lines of fusion, corresponding to the four interradial vascular lamellæ, the _ivl_ of the figures.