MEDUSID/E. r6l 



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 ver}^ feeble muscular energy, appears, on the other 

 hand, to be unceasing. Since their specific gravity considerably 

 exceeds the water in which they are immersed, these creatures, which 

 are so soft that they probably could not repose on solid ground, 

 require to keep themselves constantly moving 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 locomotion are executed by the edges of the 

 disc 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. 

 Renovated by the cessation of force in its first state of expansion, it 

 contracts itself again, and makes another movement 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 Medusre 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 

 solitar}^, 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 Medusas constitute in the Arctic seas one 

 of the principal supports of the whale. Their innumerable masses 

 sometimes cover many square leagues in extent. They show them- 

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

 epochs — alternations which depend, no doubt, on the ruling of the 

 winds and currents which carry or lead them. " The barks which 



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