84 ZOOLOGY. 
system is particularly connected with the organs of locomotion, which are 
different from those of all other animals, and are called ambulacra? (a, a, a, 
in fig. 67). They are fleshy 
and tubular, more or less 
elongated, and terminated 
by suckers. Their number 
is often very great. They 
pass through orifices in the 
external integument of the 
animal, and are generally 
arranged in rows. ‘The 
movements of the ambu- 
lacra are accomplished in 
a very remarkable manner. 
Each of these organs has 
Fig. 67.—Ambulacra of Star-fish, at its base a vesicle (0, }, 
As seen in a longitudinal and vertical section of one of in fig. 67), supplied with a 
the rays; and three of them in a separate figure on a 2 Anna 
larger scale, in which they are shewn in different W atery flu from a tube 
conditions: a, a, a, tubular feet; 5, b, 5, internal ahi ae 
vesicles; ec, the organ which supplies the fluid with which gd oe from a 
which they are filled. special secreting organ (¢ 
| in fig. 67). By the con- 
traction of the vesicles, the fluid is forced into the ambulacra, distend- 
ing them to their utmost extent; whilst on their being contracted by 
another set of muscles, it returns into the vesicles. A star-fish, or even 
a sea-urchin, can climb a perpendicular rock or the side of a glass vessel 
by means of this apparatus. The mouths of the Echinodermata are vari- 
ously furnished with masticating organs; that of the Sea-urchins has 
generally five flat calcareous teeth, moved by a very complex apparatus 
of muscles and bony sockets, which acts as a very powerful mill for 
erinding down food. 

Articulata. 
We come now to the great division of the animal kingdom called by 
Cuvier Articulata or Articulated Animals. The name refers not to the 
possession of articulated or jointed members, but to the articulated struc- 
ture of the whole body. The Articulata are composed of segments jointed 
together in a line, each segment being formed of one or more rings, which 
in some appear externally as mere folds of a soft skin, as in worms, and 
in others are covered with a hard substance similar in composition to 
the bones of vertebrated animals, as in crabs, lobsters, &. In some 
of the Articulata, the rings are almost equally developed, and the body 
is hardly otherwise divided into segments; in others, the rings differ 
1 From Latin ambulare, to walk. 
