HABITS OF THE MEDUSAE. 55 



seeing that the animals, their bodies being of greater 

 specific gravity than the surrounding water, would 

 inevitably sink were it not for the constant efforts of 

 contraction and expansion which they exhibit. They 

 swim by means of repeated approximations of the 

 margins of the disc, whereby the water contained 

 within and beneath the umbrella-like expansion is 

 forcibly driven away, and the body of course impelled 

 in the opposite direction; these efforts are leisurely 

 repeated again and again, and should the back of the 

 Medusa be horizontal, merely tend to keep it near the 

 surface of the water; should, however, the convexity 

 of the disc be inclined obliquely, by means of these 

 movements the creature rows itself about with con- 

 siderable rapidity ; nevertheless the efforts thus made 

 are very feeble, and the slightest current in the water 

 is sufficient to carry such feeble animals out of their 

 course. 



All observers agree that the Medusae feed upon 

 small animals ; and mollusca, worms, crustaceans, and 

 even fishes, are stated to constitute their ordinary 

 diet. We, however, advise any of our readers who 

 may have the opportunity of so doing, to watch very 

 closely this portion of their oeconomy; and should 

 they really be fortunate enough to feed any specimen, 

 or even to see them seize and swallow prey, to note 

 the circumstance, and thus clear up a point of no 

 small interest to the natural historian. 



Mr. C. W. Peach, in a communication read before 

 the Royal Institution of Cornwall, mentions the cap- 

 ture of a minute Acaleph, Thaumantias lucifera, 

 which had by some means caught hold of a Sagitta. 



