MOTION IN THE MEDUSA. 351 



outwards. Thus it lies quite motionless, but on the 

 slightest jar being given to the vessel, or to the table 

 on which it stands, all the tentacles at the same in- 

 stant are contracted into minute contorted balls, so 

 suddenly that it seems the work of magic. If undis- 

 turbed, however, they are quickly unrolled again? 

 almost as quickly as they were contracted. If the tenta- 

 cles when thus extended are carefully examined, they 

 are seen to be slightly club-shaped at their extremities. 



The tentacles in this species, when subjected to 

 pressure, are resolved into a multitude of minute oval 

 granules set close together, without any variation of 

 density in different parts. Their length is not more 

 than -^^ inch. I suppose these, from analogy, to be 

 filiferous capsules, though their minuteness prevents 

 me from seeing (with a power of 300) more than an 

 evanescent indication of the filiferous cavity ; and the 

 plates of the compressorium were not able to produce 

 a projection of the filament. 



The lips of the peduncle are furnished with capsules 

 exactly similar, crowded together in groups, and (as 

 it appears to me) forming little tubercles, from which 

 their points diverge in every direction. 



The motion of the Medusse through the water seems 

 to be performed on the same principle as that of the 

 larva of the Dragonfly; viz. by a jet of water forcibly 

 expelled, and impinging on the surrounding fluid. 

 In Turris, whose motions, owing to its muscular 

 development, are very energetic, the jet is very distinct 

 and strong. This appears to be the modus operandi : 

 four muscular bands, as Prof. Forbes has shown, pass 

 across the surface of the sub-umbrella, from the root 



