ACALEPHSE. 77 



seems to reside, but it is observed that the tentacuhi seem 

 to be more specially imbued with it than other parts of the 

 body. Perhaps the most remarkable property of the acalephse 

 is their phosphorescence, to which the luminosity of the ocean, 

 an appearance especially beautiful in warm climates, is princi- 

 pally due. We have more than once witnessed this pheno- 

 menon in the Mediterranean, and the contemplation of it is well 

 calculated to impress the mind with a consciousness of the profu- 

 sion of living beings existing around us. The light is not con- 

 stant, but only emitted when agitation of any kind disturbs the 

 microscopic medusse which crowd the surface of the ocean : a pass- 

 ing breeze, as it sweeps over the tranquil bosom of the sea, will 

 call from the waves a flash of brilliancy which may be traced for 

 miles ; the wake of a ship is marked by a long track of splendour ; 

 the oars of your boat are raised dripping with living diamonds ; 

 and, if a little of the water be taken up in the palm of the hand 

 and slightly agitated, luminous points are perceptibly diffused 

 through it, which emanate from innumerable little acalephse scarce- 

 ly perceptible without the assistance of a microscope. All, how- 

 ever, are not equally minute ; the Beroes, in which the cilia would 

 seem to be most vividly phosphorescent, are of considerable size ; 

 the Cestum Veneris, as it glides rapidly along, has the appearance 

 of an undulating riband of flame several feet in length ; and many 

 of the larger Pulmonigrade forms shine with such dazzling bright- 

 ness, that they have been described by navigators as resembling 

 " white-hot shot " visible at some depth beneath the surface. 

 This luminousness is undoubtedly dependent upon some phospho- 

 rescent secretion, but its nature and origin are quite unknown. 



(105.) The principal instruments of sensation in the acalephse are 

 the tentacula and suckers, which, under various forms, are append- 

 ed to different parts of the body, and which are individually capa- 

 ble of contraction and elongation to a considerable extent. In the 

 discophorous forms, these are frequently appended to the margin 

 of the disc (Jig- 27) ; sometimes they are only found around the 

 aperture of the mouth. In Porpita and Physalus they are nu- 

 merous, and hang in clusters from the inferior surface of the body : 

 but the most beautiful tentacular apparatus is that which is met 

 with in the Beroe (Cydippe) pileus; this is represented in Jig. %% ; 

 1, a, a, and consists of two very long and delicate filaments, 

 many times exceeding the length of the body when extended to 

 their full length ; from these arise others of still greater tenuity, 



