a pkil — sept. 1858.] Order Radiata. 123 



pansion propels it through the water. On the lower surface of 

 this glass-like transparent body the » mouth is to be found, or the 

 sucking organ which takes the place of a mouth, often surrounded 

 by stalk-like appendages ; and these together with the umbrella- 

 shaped body, give them much the appearance of mushrooms. 



The bodies of the Medusae are composed of cells, about as hard 

 as gristle, covered "by a tender upper skin, in which stinging organs 

 are to be found, generally similar to those of the Polypi ; indeed 

 all who are accustomed to bathing in the sea can testify to this 

 from painful experience. The disc-shaped body is of a very de- 

 cided radiate type, being always divisible into 4 or 6 complete 

 segments : — the long contractile threads which are placed on the 

 edge and seem to be used as feelers, also obey this rule. 



The nervous system and organs of sense are considered to reside 

 in certain bodies which are imbedded in the edge of the disc, 

 generally to the number of 6 or 8. They consist of some capsule- 

 shaped little bladders, in which is contained a round or angular 

 crystalline kernel. In some genera these little bladders are sur- 

 rounded by a brightly coloured pigment, which has caused some 

 observers to consider them as eyes, while others have thought 

 them a rudimentary form of ear. 



The digestive organs are formed in a very peculiar manner. The 

 mouth is generally simple, sometimes surrounded only by a raised 

 margin, but more frequently by seizing arms of the most varied 

 shapes, which often possess raised margins, formed like a ruff. In 

 some genera instead of one single mouth opening there are very 

 fine sucking-apertures, which open either into a simple middle 

 stalk, or into many feelers, which are again branched in their 

 turn. Both the simple mouth and the fine pipes which lead up 

 from these sucking apertures conduct into a larger or smaller 

 stomach cavity, which generally possesses a certain number of 

 sacks radiating from it. From these sacks spring a certain num- 

 ber of vessels which radiate towards the edge, and there disappear 

 into one of the edge-vessels, or into an extremely delicate net- 

 work of smaller vessels. In this manner the whole body is tra- 

 versed by the nourishing fluid, and not seldom the remains of 

 little animals are to be found in these canals, still undigested. 



