170 



ZOOLOGY 



SECT. 



folded along its midrib, and having more or less frilled edges : in the Rhizostoma- 

 each of the original four arms (Fig. 122, or. a.) becomes divided longitudinally in 

 the course of development, the adult members of the group being characterised 

 by the presence of eight arms, often of great length, and variously lobed and 

 folded so as to present a more or less root-like appearance. 



The arrangement of the enteric cavity and its offshoots presents an interest- 

 ing series of modifications. In the Cannostomse (Fig. 121) the resemblance to the 

 Ephyrula-stage of Aurelia is very close, the stomach giving oft eight pouches 

 which bifurcate and enter the marginal lappets. In the Semostoma? (Fig. 113) 

 the stomach lobes give off well-defined radial canals, which are frequently more 

 or less branched, often unite into complex networks, and sometimes open into a 

 circular canal round the margin of the umbrella. 



In the Rhizostomaj (Fig. 122, B) a similar network of canals is found in the 

 umbrella, but an extraordinary change has befallen the oral or ingestive portion 



st 



ff'f 



-FiG 122. Pilemapulmo. A, side view of the entire animal ; B, vertical section, diagrammatic : 

 C, one of the suctorial mouths, magnified ; c. arm canal ; g.f. gastric filaments ; gon. gonads ; 

 or. a. oral arms ; rod. c. radial canal ; s. mth. suctorial mouths ; st. stomach ; tl, tS.tS, tentacles 

 on oral arms. (After Cuvier, Claus, and Huxley.) 



of the enteric system. Looking at the oral or lower surface of one of these Jelly- 

 fishes, such as Pilema, no mouth is to be seen, but a careful examination of the 

 oral arms shows the presence of large numbers hundreds, or even thousands in 

 some cases of small funnel-like apertures (B, C, s.mth.) with frilled margins. 

 Rhizostomes have been found with prey of considerable size, such as fishes, em- 

 braced by the arms and partly drawn into these apertures, which are therefore 

 called the suctorial mouths. They lead into canals in the thickness of the arms 

 (B, c.), the lesser canals unite into larger, and then finally open into the stomach 

 (at. ). We thus get a, polyatomatow or many-mouthed condition which is practi- 

 cally unique in the animal kingdom, the only parallel to it being furnished 

 by the Sponges, in which the inhalant pores are roughly comparable with the 

 suctorial mouths of a Rhizostome. 



