216 THE OCEAN WOULD. 



ported by the waves in innumerable swarms from the coast of the 

 Atlantic to the region of whales. " The locomotion of the Medusae, 

 which is very slow," says De Blainville, "and denotes a very feeble 

 muscular energy, appears, on the other hand, to be unceasing. Since 

 their specific gravity considerably exceeds the water in which they are 

 immerged, these creatures, which are so soft that they probably could 

 not repose on solid ground, require to agitate constantly in order to 

 sustain themselves in the fluid which they inhabit. They require also 

 to maintain a continual state of expansion and contraction, of systole 

 and diastole. Spallanzani, who observed their movements with great 

 care, says that those of translation are executed by the edges of the 

 disk approaching so near to each other that the diameter is diminished 

 in a very sensible degree ; by this movement a certain quantity of 

 water contained in the body is ejected with more or less force, by which 

 the body is projected in the inverse direction. Kenovated by the 

 cessation of force in its first state of development, it contracts itself 

 again, and makes another step in advance. If the body is perpendicular 

 to the horizon, these successive movements of contraction and dilatation 

 cause it to ascend ; if it is more or less oblique, it advances more or 

 less horizontally. In order to descend, it is only necessary for the 

 animal to cease its movements ; its specific gravity secures its descent." 



It is, then, by a series of contractions and dilatations of their bodies 

 that the Medusae make their long voyages on the surface of the 

 waters. This double movement of their light skeleton had already 

 been remarked by the ancients, who compared it to the action of 

 respiration in the human chest. From this notion the ancients called 

 them Sea Lungs. 



The Medusae usually inhabit the deep seas. They are rarely 

 solitary, but seem to wander about in considerable battalions in the 

 latitudes to which they belong. During their journey they proceed 

 forward, with a course slightly oblique to the convex part of their 

 body. If an obstacle arrests them, if an enemy touches them, the 

 umbrella contracts, and is diminished in volume, the tentacles are folded 

 up, and the timid animal descends into the depths of the ocean. 



We have said that the Medusae constitute in the Arctic seas one of 

 the principal supports of the whale. Their innumerable masses some- 

 times cover many square leagues in extent. They show themselves 

 and disappear by turns in the same region, at determinate epochs 



