282 XATURAL HISTORY. 



One of the prettiest free-swimming Medusoids is more or less bell-shaped, but it has a stalk-like 

 top, by which it can attach itself to weed or rock, and the margin of the bell is separated into eight 

 knobs, or lobes, covered with tentacles. The membrane of the bell is festooned between the lobes, 

 and the whole animal is very transparent. These Lucernariae are very contractile, and can change 

 their shape, and their movements are most varied. They swim by contractions and expansions of the 

 disc, like ordinary Jelly-fish; but when they settle down, the lower part of the disc curves up and the 



body is fixed on its peduncle. L. Agassiz, in his charming 

 book on the marine animals of Massachusetts Bay, writes: 

 "It frequently secures itself in the upright position, 

 spreading itself in the form of a perfectly symmetrical cup 

 or vase, the margin of which is indented by a succession of 

 inverted scallops, the point of junction between two 

 scallops being crowned by a tuft of tentacles. But watch 

 it for a while, and the sides of the vase turn backward, 

 spreading completely open, till they present the whole 

 REPRODUCTION OF DiscopHORA. inner surface, with the edges even curved a little down- 



ward, drooping slightly, and the proboscis rising in the 

 centre. In such an attitude one may trace, with care, the shape of the mouth, 

 the lobes surrounding it, as well as the tubes and cavities radiating from it 

 towards the margin. A touch is, however, sufficient to make it close upon 

 itself, shrinking together, or even drawing its tentacles in and contracting 

 all its parts, till it looks like a little ball hanging on the stem. These are but 

 few of its manifold changes, for it may be seen in every phase of contraction 

 and expansion." 



The bell is not a hollow hemisphere, but is a mass of gelatinous hardness, 

 and the peduncle is an extension of the bell, and it has a minute disc at the 

 end, for attachment. The mouth is in the midst of the bell, which has an 

 inverted look, is square, and is on a projecting proboscis. The body-cavity 

 is four-chambered, and each communicates with the mouth. Triangular-looking 

 structures pass outwards to the tentacular knobs, and are the ovaries, consisting 

 of a number of little bags, each crowded with eggs. These drop into the 

 stomach, and are passed out of the mouth. The tentacles are club-shaped, LUCERXARI.*: ON PIECE OF 

 and they have an orifice which leads through a canal to the chambers of the SE ^y E (Lucemaria octo- 



raaiata) . 



digestive cavity, two of the clusters being connected with each chamber. 



"Their chief office," writes L. Agassiz, "is to catch food and convey it to the mouth ; but the Lucer- 

 naria frequently uses them in locomotion, fixing itself by them, and loosing the end of its peduncle." 

 Between the clusters are slight projections, which are short and compact, and they are used as 

 claspers to a certain extent. They contain a slight pigment spot, which may be an eye. The colour 

 of the American form (Lucernaria auricula) is greenish, with a faint tinge of red, and it assumes a 

 beautiful aquamarine tint. The British species thrive in aquaria, and are very beautiful objects. 



ORDER SIPHONOPHORA.* 



These are free- swimming Hydrozoa, but each one consists of a colony or assemblage of individuals 

 united in a common stock, termed a hydrosoma,f and placed under a more or less tough part, which acts 

 as a float. This last may be large and crested, or it may be small, and united to others which fulfil the 

 same office. An air-sac, from which air can be expelled, enters into the composition of the float. 



Nutritive and generative individuals, or zooids, exist in the colony, and long pendant tentacles 

 add to the beauty of the forms. In some an oil bubble, surrounded by tissue, acts as a float. They 

 reproduce by developing buds, which give forth plaiioblasts (wandering buds) or medusae. These 

 develop eggs, which grow into the shape of the float and colony. 



The "Portuguese Man-of-War"| may be seen in the tropics sailing on the surface of the sea, it? 



* Tube, or siphon -bearers. f See Note on p. 286. J Physalia utriculus. 



