HYDROZOA. 



59 



a fringe of fine tentacles on those invervening portions, the ends of Case 3, 

 the bifid arms now occupying the notches in the rim and forming Upright jmrt. 

 the lappets of the sense-organs ; the medusa is now recognisable as 

 Aurelia. 



The fixed Scyphistoma stage is not common, many Scypho- 

 medusfe developing direct from the egg. The Scyphomedus^e are 

 divided into four Orders. The first Order includes the exceptional 

 Lucernarm-Halichjstiis {Luceniaria) ocioradiatus * (Fig. 22) is shaped 

 like a vase with a short stem. The upper edge is produced into 

 eight arms each crowned with a tuft of tentacles. The animal, 

 which fixes itself by its stalk, can creep along or swim. On the 

 margin, between the tufts of tentacles, are peculiar modified tentacles 

 known as anchoring bodies, which assist progression by sticking to 

 and grasping the surface of the sea-weeds or stones. The mouth 



Fk;. 22. 



Ilaliclydus octoradiatus, a Lucernarian IMedusa, on sea weed, a, mouth 

 and stomach ; h, tentacles ; c, ancliors ; d, reproductive glands. ( J'rom 

 Johnston's British Zoophytes ; figures slightly altered. ) 



and stomach (manubrium) are in the centre. Halidystiis, which is 

 commonly found adhering to sea-weeds, varies in colour, being olive- 

 brown, green, or pink. The second Order (Discomedusae) includes 

 the commoner kinds of Jelly-Fish, Pelagia, Aurelia, Pilema, Coty- 

 lorhiza, &c. (see Case 3). In Pihma (Fig. 23) and other " Rhizo- 

 stomatous " forms the lips and arms of the manubrium are fused 

 together, and the food, consisting of minute marine organisms, is 

 taken in through little suctorial mouths and conveyed up long 

 canals. Pihma octopus * is fairly common. Specimens often attain 

 a diameter of two feet. The greenish umbrella has a purple frill- 

 like margin ; there are eight tentaculo-cysts with their special 

 lappets, but there are no tentacles round the margin of the 

 umbrella. The large mouthles^s manubrium breaks up into eight 

 long arms often attaining a length of two feet ; the minute, 



Case 3, 

 Upright part. 



