TYPES OF C(ELENTERA AURELIA AURITA. 153 



canals, and is ciliated throughout. The mesogloea is a 

 gelatinous coagulation containing wandering amoeboid cells 

 from the endoderm. The whole animal is very watery; 

 indeed, the solid parts amount to not more than 10 per 

 cent, of the total weight. Yet some jelly-fish (species of 

 Rhopikmd) are used as food in Japan ! 



Nervous system. The nervous system consists (a) of a 

 special area of nervous epithelium, associated with each of 

 the eight sense organs, and () of numerous much-elongated 

 bipolar ganglion cells lying beneath the epithelium on the 

 under surface of the disc. This condition should be con- 

 trasted with the double 

 nerve -ring in Craspedote 

 medusoids, but too much 

 must not be made of the 

 contrast, for a nerve-ring 

 is described in Cubo- 

 medusae, one of the orders 

 of Acraspedote jelly-fish. 

 In Aurelia the sense organs 

 are less differentiated than 

 in many other jelly-fish. 

 Each of the eight organs, 

 protected in a marginal 

 niche, consists of a pig- 

 mented spot, a club-shaped 



projection With numerOUS 

 CalcareOUS " Otoliths " in 

 itS Cells, and a COUple Of 



apparently sensitive pits or 

 grooves. The sense organs arise as modificatioris of 

 tentacles, and are often called " tentaculocysts " or "rho- 

 palia." Their cavities are in free communication with 

 branches of the radial canals. 



Muscular system. Between the plexus of nerve cells 

 and the sub-umbrellar mesoglcea there are cross-striped 

 muscle fibres, each of which has a large portion of non- 

 contractile cell substance attached to it. They lie in ring- 

 like bundles, and by their contractions the medusa moves. 

 Unstriped muscle fibres are found about the tentacles and 

 lips. 



FIG. 73. Surface view of Aureha. 

 From Romanes. 



Showing four genital pockets in centre, 

 much branched radial canals, eight peri- 

 pheral niches for sense organs, and peri- 

 pheral tentacles. 



