140 CLASS IV. 
effected by means of these muscular fibres, and in no degree by 
forcing fluid into and out of them. To how great an extent these 
parts ean be elongated may be judged by the length of the spines 
of the shell in sea-urchins: they must have the power of extending 
beyond the longest spines. In specimens that have been kept in 
spirits these tubules are found to be short and mutually entangled. 
The teeth, and the curious apparatus that encloses them (ARISTOTLE’S 
Lantern) have a number of proper muscles. As to the general 
muscular system, that which moves the whole body, it is found 
especially developed in Holothurie. Here ten muscles run the whole 
length of the body, beneath the skin: they are arranged in pairs, 
which are separated by spaces in which transverse circular fibres are 
found that cover the entire inner surface of the skin. By means of 
the longitudinal muscles the body can be shortened and bent: by 
the transverse fibres it is contracted transversely, and so attenuated 
and elongated. The longitudinal muscles are inserted into a cal- 
careous ring composed of five large and five smaller pieces, and 
surrounding the commencement of the intestinal canal. 
All these animals inhabit the sea. They are found in all parts 
of the world: yet, most of the species only in limited regions. Since 
we have only a partial acquaintance with foreign species, many 
more of which will doubtless be hereafter discovered, we are not in 
a condition to give a survey of the geographical distribution of the 
genera. Unlimited confidence is not to be reposed in the accounts 
given by some writers of the localities in which the species are 
native. Of the Asterie nearly one-third of the known species are 
found in the East-Indian seas, one-fifth in the seas of Europe. Of 
Ophiure, on the other hand, the European and African species 
are more numerous than the East-Indian. The western hemisphere 
has, on the whole, fewer star-fishes than the eastern: in America 
there are no species of Scytaster, as, for instance, of Culcita, Astro- 
gonium, Stellaster ; Echinaster, on the other hand, is peculiarly 
American. The species of Huryale are chiefly found in the Arctic 
and in the Indian seas. ‘To the species which are very generally 
distributed belones that which occurs on the coast of Holland, 
Asterias (Asteracanthion) rubens. The Red sea so rich in species of 
the class of Polyps, has only a comparatively small number of star- 
fishes, and, in this respect is much behind the Mediterranean, which 
is especially rich in species of Astropecten. The Baltic appears to be 
