750 THE ANIMAL KINGDOM. 



in the Solmaridae, globular. The tentaculocyst is frequently borne upon 

 an auditory ectodermal papilla composed of sense-cells with long auditory 

 hairs. * Otoporpae,' or meridional streaks of ectodermal cnidoblasts ex- 

 tending centripetally on the exumbrella from the bases of the tentaculocysts 

 are found in the Cunanthidae and Peganthidae. 



A prominent manubrium is present in some Ctmanthidae and in many 

 Aeginidaefa\& not in other instances. In the last-named the mouth is generally 

 four lobed : it is always extremely dilatable. The central stomach cavity is 

 usually flattened. In the Cunanthidae it is produced into radial pouches, 

 a pouch corresponding to each tentacle. Every pouch is connected to the 

 pouch on either side by a separate * festoon ' or loop-canal, which follows the 

 edge of the corresponding lobe. The two festoon canals originating from 

 each pouch are separated at their roots by a peronium. The PegantJiidae 

 have a central stomach and festoon canals derived from it corresponding 

 to each lobe : the Aeginidae a variable number of interradial pouches ex- 

 tending into each lobe, and festoon canals derived from the central 

 stomach as well. In the Solmaridae the festoon canals are obliterated : 

 the stomach may be simple and central, or prolonged into radial or inter- 

 radial pouches. 



The sexual organs are developed on the subumbrellar aspect of the 

 stomach, either as a simple ring which may extend in some Cunanthidae 

 either on to the radial pouches, or become restricted to them. The ring 

 may be resolved in some Peganthidae into a number of separate interradial 

 pouches, as it always is in Aeginidae. In Solmaridae all three conditions 

 may obtain. 



Most Trachomedusae have a firm, stiff, semi-globular, or broad bell. 

 In the Aglauridae, however, it is bell-shaped, cylindrical, or eight-sided and 

 prismatic ; and the exumbrella is excessively thin. The velum is broad 

 and stout, and hangs downwards when the Medusa is floating. The margin 

 of the exumbrella has a strongly developed ring of cnidoblasts, and where 

 the solid tentacles are sub-marginal, as in all Geryonidae and some Peta- 

 sidae, there are peronia, beneath which the roots of the solid tentacles, when 

 cast off, persist in connection with the circumferential canal. The ex- 

 umbrella is prolonged in the Aglauridae and Geryonidae into a long 'gastric 

 peduncle,' a solid cylindrical process of its gastric aspect, which is in the 

 last-named usually longer than the height of the bell, and therefore projects 

 from the bell-cavity. Mesogonia occur in the Pectyllidae : see p. 786. 



The tentacles are usually numerous, and may even be disposed in 

 several rows one above the other. Eight, four radial and four interradial, 

 occur in some instances, four radial in Petasus alone, reduced to two in 

 Dipetasus. The primitive tentacles are always solid, but radial hollow 

 tentacles communicating with the circumferential canal are present in 

 Olindias and Pectanthis % and appear in the Geryonidae in the course of 



