Royal Physical Society. 233 



sub-umbrella, and the bud has become a perfect Acaleph, 

 (fig. 9), although still joined by a narrow pedicle to the poly- 

 pary of the Eudendrium. This pedicle is, however, soon 

 absorbed, the thin covering of the corallum bursts, and the 

 living bubble dashes away through the water, with powerful 

 strokes, a formidable little tyrant of the sea. 



When first separated from the Zoophyte, the Acaleph seeks 

 the surface of the water with long zig-zag bounds, carrying its 

 tentacles closely coiled in spirals. Having remained swimming 

 there for a short time, it begins to sink slowly with the mouth 

 of its bell uppermost, and the tentacles, uncoiling themselves, 

 stream behind, to a distance of more than twenty times the 

 length of the bell, in straight lines or graceful curves, sweep- 

 ing the water in search of prey. In most of the naked-eyed 

 medusae, the umbrella is so thick and solid, that the shape of 

 the upper part of the bell is but slightly altered by the con- 

 tractions of the sub-umbrella ; but in the species I am now 

 describing the umbrella is thin and soft, so that the whole 

 parietes of the bell contract together at each stroke, forming a 

 curve similar to the wave-line of Scott Russell, and admir- 

 ably adapted for rapid passage through the water. 



A jar of these lively creatures, some swimming rapidly 

 about like small frogs, with their half-coiled tentacles jerking 

 backwards at each stroke, others descending headlong in flocks, 

 like the falling train of a rocket, and all glittering under 

 oblique illumination in the dark water, forms one of not the 

 least interesting of those scenes of beauty which are of daily 

 occurrence to the naturalist. 



12. In the Anatomy of the Acaleph of Eudendrium four dis- 

 tinct parts claim our notice. 



(1.) The umbrella. 



(2.) The sub-umbrella. 



(3.) The lateral and circular canals. 



(4. J The alimentary polyp or peduncle ; and 



(5.) The tentacular polyps. 



13. In the description of these parts, I shall consider the 

 animal, not as a sexual polyp, with Ehrenberg, Allman, Car- 

 penter, and others, but as a free and independent extension of 

 the polypary of Eudendrium ; not as the product of the alternate 



