232 Proceedings of the 



frequent intervals, from about one-eighth to a quarter of 

 an inch in height, and bearing at their summit small white 

 club-shaped polyps. The polyp is capable of partially re- 

 treating into the upper part of the tube, which is dilated at 

 this point so as to form an imperfect cell. The filiform ten- 

 tacles vary in number from four to twelve, according to the age 

 of the polyp, and are held in two rows, the one (generally con- 

 sisting of four) elevated, the other depressed or horizontal. 



At almost all seasons of the year we notice on the polyp- 

 hearing stems of this Zoophyte small protuberances, which 

 rapidly increase in size, and become Medusae or "jelly-fish" of 

 the naked-eyed type. 



The Medusa-bud first appears as a diverticulum or sac 

 of the endodermic and ectodermic layers of the polypary, 

 covered by an extension of the corallum. After a short period 

 the diverticular sac becomes depressed at its summit, and at 

 the bottom of the depression a slight elevation may be observ- 

 ed. This depression and elevation are the rudiments of the 

 umbrellas and peduncle of the future medusa or acaleph. 

 The depression rapidly deepens, until the sac becomes folded 

 in upon itself, so as to form a deep bell with the peduncle rising 

 like a thick clapper from the bottom of its concavity. In the 

 mean time the endoderm of the bell (now become very opaque 

 by the deposit of red granular matter within it) has slightly 

 separated from the outer layer of ectoderm, and has become 

 divided into four thick tubular lobes, communicating with each 

 other by a circular canal at their summits, and with the pe- 

 duncle at their bases, and connected together laterally by the 

 inflected ectoderm, within which a transparent muscular mem- 

 brane is developed. The ectoderm now forms the umbrella and 

 the endodermic lobes, with their uniting membrane, form the 

 lateral canals, and the sub-umbrella of the Acaleph or Me- 

 dusa. A constant interchange of circulating particles takes 

 place between the cavity of the parent polypary and the 

 cavities of the peduncle and the endodermic lobes. The pro- 

 cess of development goes on, the peduncular sac is changed 

 into a quadrangular polyp, the endodermic lobes into slender 

 canals, bearing at their extremities polyps of a peculiar form, 

 systolic contractions commence in the muscular tissue of the 



