CTENOPHORA. 201 



and below. The perradial vessels give rise, close to tlieir origin, 

 to the paragastric canals, which run oralwards on each side of the 

 stomach (Fig. 157). They end blindly, and are absent only in one 

 genus (Euchlorci). The tentacular vessels are direct continuations 

 of the perradial vessels (Fig. 158, fg). The funnel is continued 

 upwards as the funnel-vessel, which divides beneath the sense- 

 organ into two limbs, each of which again divides into two ampullae, 

 one situated in each quadrant of the body. Two of these ampullae 

 (and two which lie in diagonally opposite quadrants) open to the 

 exterior by small pores placed just outside the sensory plate 

 (Fig. 159 I, ex). 



There are two extensile tentacles (Fig. 157) in the funnel-plane. 

 They consist of a stout base contained in a depression of the body- 

 wall, which constitutes the tentacular sheath and into which the 

 tentacle can be withdrawn. The tentacle vessel is not prolonged 

 along the tentacle, but ends in two ampullae at its base. The tentacles 

 carry a row of branches which are provided with the peculiar adhesive 

 cells (Fig. 161). 



The muscular tissue is feebly developed. It has the form of fibres, 

 lying in the jelly and branched at both ends. 



There is a sub-epithelial nervous plexus with scattered ganglion 

 cells. It extends on to the stomach, but no connection has been 

 observed between it and the sense-organ and ciliated grooves and 

 ribs. 



The description given above applies to one group of the Ctenophora, 

 the Cydippidae, the structure of which may be taken as typical. 

 There are, besides, the Cestidae, the Lolxttae, and the Beroidae, 



The Cy<lippidae include, besides the spherical form just described, 

 forms in which the main axis is elongated (cylindrical Pleuro- 

 bracliiadae'), and forms in which the body is compressed in the stomach- 

 plane, i.e., the stomach-axis is much reduced (Euclilora, Cattianira}. 

 In Cattianira (Fig. 165) there are two wing-like processes of the 

 aboral end of the body; they lie in the funnel-plane, and the 

 meridional vessels are prolonged into them. In Euclilora the sub- 

 tentacular ribs are longer than the sub-stomachal. 



The larvae of the Cestidae and Lobatae closely resemble the above 

 described typical form (particularly the Mertensid variety of it) and 

 acquire the adult condition by a complicated metamorphosis (see 

 below). 



The Cestidae are ribbon-shaped (Fig. 160), and the body is 

 enormously elongated in the stomach-plane and much compressed 



