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the under-side of the arms like star-fish, but have little openings 

 through which the tube feet pass ; in this class it is the arms them- 

 selves and not the tube feet that are used for locomotion. The 

 arms of the brittle-star are nearly always five in number, and 

 unbranched except in the family Astrophytidse, where the numerous 

 branches interlace and form a kind of basket-work all round the 

 disc, whence the animals are called basket-fish or medusa head star- 

 fish. Ophiuroids live on the smaller Foraminifera ; they appear to 

 have great facility for voluntarily throwing off a part or the whole 

 of a ray or several rays, which can be reproduced by new growths. 

 We now come to the Echinoidea or sea-urchins, in which the rays 

 are not free, but unite to form a compact spherical heart or disc- 

 shaped test covered with rounded tubercles of various sizes, to which 

 spines are attached by a ball and socket joint, disposed chiefly in five 

 broad zones, alternating with which are five narrower zones with 

 fewer tubercles and pierced by small holes, through which pass the 

 tube feet, all provided with suckers. The test (or shell, as it is 

 commonly called, although it does not by any means correspond in 

 structure with the shell of a Mollusc) is composed of a great number of 

 small hexagonal plates, the edges of which are fitted closely together, 

 so that the whole shell is converted into a water-tight box ; besides the 

 spines there are very many pedicellarise or pincers (as in the common 

 star-fish), as well as the madreporic tubercle or filter already men- 

 tioned. Turning over would appear to be a matter of considerable 

 difficulty to this animal. A long series of exhaustive experiments 

 were made on this creature by Romanes, and he tells us that unless 

 the animals are fresh and vigorous they are unable to right them- 

 selves at all, and remain inverted until they die. Their method of 

 turning is always the same : two or three rows of suckers are protruded 

 and fastened firmly to the floor, their combined action serves to tilt 

 the globe slightly over, enabling the next row of feet to touch the 

 floor, and when they have secured their hold they assist in increasing 

 the tilt, then the next feet in the series lay hold, and so on until the 

 globe slowly rises on its equator ; as soon as this position has been 

 attained, it might be anticipated that the Echinus would simply let 

 go all its attachments and allow itself to roll over into its natural 

 position, but it seems to be afraid of being rolled about at the mercy 

 of currents, and therefore in this case it lets itself down almost as 

 slowly as it raised itself up ; so gently, indeed, is the downward move- 

 ment effected that an observer can scarcely tell the precise moment 

 at which the righting is concluded. 



Holothuria or sea-cucumber or sea-slug : the body is cucumber- 

 shaped, with the mouth at one end and the vent at the other ; it has 

 no rays or arms, but its mouth is surrounded by a circlet of tentacles 

 often branched, which can be retracted at will ; they usually attach 

 themselves to rocks by their tube-feet, and wave the tentacles about. 

 These slugs are collected in large quantities throughout the Indian 

 Archipelago, and are eaten by the Chinese and Malays ; the food is 



