REPORT ON THE SIPHONOPHOR^. 87 



The Centradenia (fig. 4, uc; fig. 7), or the so-called liver, is a lanceolate gland, the 

 upper convex surface of which is flatly conical, and fills up the inferior concave face of 

 the pneumatocyst (fig. 4, pf). Its lower flat horizontal face forms the roof of the central 

 siphon, and is separated from its hase by the gastrobasal plate, a thick structureless 

 fulcrum (fig. 4, st). The periphery of this plate is pierced by sixteen radial main canals, 

 which arise from the lanceolate base of the central siphon in two longitudinal rows, 

 and run along the subumbrella towards its margin ; they give off at their base sixteen 

 ascending liver-canals, which run in the convex upper surface of the centradenia towards 

 its conical apex, where they unite and form a central " liver-star." Very numerous 

 lateral branches, which arise everywhere from these main canals, penetrate into the solid 

 exodermal parenchyma of the centradenia, and form a very dense network by innumer- 

 able anastomoses. The vessels in the upper and outer (hepatic) part of the central 

 gland are dark brown or black, thickly filled with pigment-granules (fig. 4, uh), except 

 the uppermost ; whilst the canals in the lower and inner (renal) part are white or 

 colourless, and contain numerous small greenish guanin-crystals (fig. 4, un). 



Central Siphon (fig. 2 ; fig. 4, sa ; fig. 7, sa). — The large central polypite is inversely 

 conical, sharply compressed from both sides, very contractile, and variable in form and 

 size. Its lanceolate roof is nearly half as large as the adjacent basal face of the centra- 

 denia, and separated from it by the structureless fulcrum or the gastrobasal plate. Its 

 muscular wall is very thick, and exhibits in some specimens outside eight or sixteen thick 

 longitudinal ribs, which are prominent inside as deep grooves. The opening of the mouth 

 has often eight triangular lips (fig. 4, so). 



The periphery of the lanceolate base of the central siphon exhibits sixteen openings, 

 which conduct into the sixteen radial main vessels of the subumbrella ; two opposite of 

 these gastral canals lie nearly in the sagittal axis of the subumbrella (one ventral and 

 one dorsal), and these are much wider and longer than the fourteen other vessels which 

 arise symmetrically from both sides (fig. 7). 



Canal System (fig. 7). — The reticular system of anastomosing gastro-canals, which 

 arise from the branches of the sixteen above-mentioned radial main canals, is in this, as 

 in other large Velellidae, very complicated. The following principal branches may be 

 distinguished : — (l) The sixteen ascending superficial canals, which pass off from the 

 former immediately at their origin, and end centripetally in the upper face of the 

 centradenia ; (2) very numerous canals which form a dense reticulum in the sub- 

 umbrella ; (3) numerous vessels which arise from the peripheral part of the centradenia, 

 and enter into the gonostyles ; (4) a smaller number of vessels, outside the latter, which 

 open into the tentacles ; (5) a corona of radial submarginal vessels which run in the 

 peripheral part of the subumbrella, between the tentacular zone and the margin ; these 

 open into (6) a marginal ring-canal, which runs inside the series of marginal glands ; 

 (7) a coronal canal, or inner submarginal ring-vessel, runs in the furrow between 



