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of much upward or downward movement. It is somewhat 
remarkable that although many of the species have arms many 
times longer than the bodies are broad, and they seem to be 
of the greatest possible importance to them, still they are not 
only readily broken by accident, but even cast off joint after 
joint, piece after piece, until only the body is left. These kinds 
have the very good name of Brittle Stars. Other Ophiurans 
have small spines on the arms, have not so much horizontal and 
about the same amount of vertical movement as the others, and 
their power of casting loose their own segments is less. These 
are the Sand Stars. Both kinds have the arms in numerous 
joints, each of which consists of four plates. One is above — the 
upper arm plate ; one is below — the lower arm plate ; and one on 
either side, and encroaching more or less above and below (or not 
at all), the two side arm plates. The plates get smaller and 
smaller towards the narrow tip of the arm, and the whole mem- 
ber consists outside of a repetition fore and aft of these four 
plates. Sometimes skin exists instead of some plates or parts of 
plates, and the successive plates are united by skin to their 
neighbours. The plates are not very thick, and form, as it were, 
a tunnel, wide, close to the body, and narrowing at the tip, where 
it is closed. There is a central support running down inside the 
arm, which can be seen when an arm is broken across, and cer- 
tain openings in the arm outside have to do with it. The open- 
ings are on either side of each lower arm plate, and between it 
and the side arm plate on either side, and they are for the pas- 
sage outwards from within of feelers or tentacles. The arms are 
flat below, where covered by the lower arm plate, rounded, and 
more or less tall at the sides, where the side arm plates and the 
spines are, and rounded or roof-shaped above, from the presence 
of the upper arm plates. It must be remembered that the ten- 
tacles come out below at the sides of the lower arm plates ; 
and they are protected by a little scale or scales, which may 
be on the side arm plates, or on the lower arm plates, or on 
both. On looking at the mouth of a living Ophiuran, four 
longish tentacles will be seen in each slit which is between 
two mouth angles, and two belong to the jaw of each side of 
each angle, so that every jaw has four, or two on either side. 
One is higher up in the jaw than the other, and they are pro- 
tected by tentacle scales more or less large. (Figs. 4, 9.) The 
passage between the teeth leads to the stomach. One of the 
group in lively movement is a sight to see ; the muscular 
energy is marvellous, and this is especially the case with the 
Brittle Stars. A Sand Star may be seen crawling over things 
in the aquarium, moving its arms not very much, but using 
the numerous pairs of short active tentacles a good deal. They 
have no suckers at the end, and they are not attended by care- 
