24 Invertebrate Zoology. 



tentaculo cysts, or rhopalia. Each sense-organ is borne in a 

 median sinus of one of the eight large lobes, four perradial, 

 and four interradial. 



Four perradial pillars are now to be observed as supports 

 of the angles of the mouth. They are arranged radially, and 

 at their proximal ends rest against the circular muscle of the 

 subumbrella. This muscle is a broad, flat band of parallel 

 fibres extending as a circle midway between the mouth and 

 the margin. A pair of radial muscles extend into each of 

 the eight lobes from near the peripheral edge of the circular 

 muscle. There are, then, sixteen radial muscles, four 

 pairs of perradial and four pairs of interradial. 



Between each pair of contiguous perradial and interradial 

 muscles (adradiaUy) a collection of highly contractile ten- 

 tacles will be noted. These tentacles take their origin from 

 near the peripheral edge of the circular muscle, and, during 

 life, may be extended to an enormous degree. They are 

 richly supplied with nematocysts and are the more essential 

 prehensile organs. 



The sexual glands (ovaries or testes} are four large lobu- 

 lated organs located interradially and separated from each 

 other by the perradial pillars. 



The velum, characteristic of the Hydromedusse, is not 

 generally present in the Scyphozoa, and the term Acraspeda 

 has hence been applied to the members of this group in dis- 

 tinction to the term Craspedota as defined for the Campanu- 

 larian medusoid. 



Digestive System. If a blunt probe is passed through 

 the oral opening, the oesophagus will be found to be short, 

 and, in cross-section, quadrangular. The openings into the 

 four spacious interradial reproductive sacs lead from the 



