APRIL — -sept. 1858.] Order Radiata. 



133 



stiff little hair. These are only to be seen with the microscope, 

 but there are also rib -like lines on the surface of the body, on 

 which the swimming organs are placed. These consist of long 

 stiff hairs placed in oblique lines, which are sometimes united at 

 their base and are moved backwards and forwards in swimming 

 singly and in union they depend altogether on the will of the ani- 

 mal. These swinging ribs scintillate with the motion of the ani- 

 mal in the most beautiful prismatic colours, and one may see 

 clearly how the animal by oblique turns and twists sometimes uses 

 this edge, sometimes that, leaving the others at rest. Thus these 

 animals progress through the water with their slightly contractile 

 bodies, without any other visible motion. 



The digestive-apparatus of the Rib-medusae is exceedingly sim- 

 ple. The mouth is to be found in the axis of the body, and leads 

 immediately or by a longer contraction into a large cavity, the 

 stomach, which in its turn contracts, and debouches by two side 

 fissures into a funnel-shaped hollow, which is intended for taking 

 in water. The mouth is generally furnished with very long, ex- 

 tremely contractile seizing threads, which are branched, and usually 

 lie in peculiar sheaths inside the body where they are in constant 

 worm-like motion. These threads are armed with organs both for 

 stinging and poisoning which it appears that they use against their 



P re y- 



Above this funnel shaped cavity lies the simple ganglion, from 

 which distinct branches radiate on all sides, and on which is placed 

 a little bladder, in which a quantity of crystalline calcareous parti- 

 cles are kept in tremulous motion ; we must therefore consider it 

 as the rudiment of an ear-bladder, Other nerves and organs of the 

 senses there are none. From the funnel-shaped cavity spring ca- 

 nals which run along the ribs of the swimming-flaps and show a 

 tremulous motion in their inside ; — these may be for leading in 

 water, or they may be breathing organs, of which we otherwise 

 discover not a trace. 



The organization of these animals which are to be found in num- 

 bers in every sea is so uniform that there is no need to divide them 

 into different orders. We distinguish two families:— 



