CASSIOPEA XAMACHANA. 205 



disc that the canals are provided with oral funnels. For most of their course on the disc 

 the canals give rise to the very small vesicles, finely speckled with a reddish brown 

 pigment, that already have been mentioned. These have nettle batteries at their tips, 

 and are so numerous as to cover completely the greater part of the disc and to hide the 

 course of the canals. This mass of small vesicles, however, is not acquired until late. 

 Specimens as much as 6 cm. in diameter will be found to be without them. In such 

 specimens we have the five largest vesicles, and a number of oral funnels are scattered 

 along the canals, just as they are upon the arms. This replacement of the oscula on the 

 oral disc by small vesicles has been observed to occur also on adult females of Polyclonia 

 frondosa, but not in the males (Bigelow, '93) . It is not improbable therefore that a 

 similar difference between the sexes may be discovered in our species of Cassiopea. 



The Subgenital Cavities and the Digestive Tract. At each of the four points 

 of junction of the brachial canals there is a slit-like passage, oesophageal canal, dipping 

 vertically into the mesogloea of the disc, and opening into the stomach. The latter is 

 a lens-shaped cavity, with a gently arched roof. Its floor consists chiefly of four lozenge- 

 shaped areas, where the body wall is very thin and plaited in radial folds (Fig. 34) . 

 These thin parts of the 'body wall form the roofs of the subgenital cavities, which open 

 to the exterior, each by an elliptical orifice, osteum, (x, Fig. 34) in the side of the oral 

 disc near the subumbrella and in the angle between two pairs of arms (interradial) . 

 The gonad appears as a band which crosses this membrane tangentially at its greatest 

 width. Just central to each gonad there is a multiple series of very many small gas- 

 tric filaments forming a narrow band parallel to the ovary. These are ciliated, and 

 provided with nettle and gland cells. The portion of the floor of the stomach not made 

 up of these lozenge-shaped membranes is bounded by the firm mesogloea of the oral disc. 

 This area has the shape of a Maltese cross, and it is in the arms of this cross, between the 

 subgenital cavities, that the passages from the oral canals open into the stomach. 



Near its periphery the floor of the stomach is marked by radial grooves. These are 

 continued, each into one of the radial canals that extend outward from the edge of the 

 circular stomach to the marginal region of the umbrella. There are regularly thirty-two 

 of these, sixteen in the radii of the rhopalia, and sixteen interrhopalial. When the 

 number of rhopalia is increased, the number of radial canals may or may not increase in 

 proportion. There are often thirty-four or thirty-six of them. The canals in the 

 radii of the rhopalia are larger and more nearly straight than the interrhopalial ones, and 

 all are connected by a fine network of anastomosing branches, among which no distinct 

 circular canal can be recognized. The meshes in the network of canals are connected by a 

 plate of endodermal cells, the endodermal lamella. This lamella is also in contact with the 

 subumbrellar ectoderm along a line encircling the umbrella a short distance from its mar- 



