FCBINODERMATA. 
205 
L 
at| d disposition of 'which serve to characterise the genera and the 
s Peeies. 
Another species, Asterias aurantiaca , will give an exact idea of the 
general type of animals of this order. This zoophyte, which is repre- 
sented in Fig. 106, is common in the northern seas; it has five rather 
"~ l g arms, furnished with spines which are of an orange colour— hence 
MJ ° name. When we see one of these animals stranded upon the 
it appears to he entirely destitute of all power of progression. 
!llt the star-fish is not always immovable; it is provided with an 
a Pparatus for locomotion, which appears to serve at the same time the 
Imposes of respiration ; for Nature is very economical in her gifts to 
least-organised beings ; she bestows upon them feet, with respiratory 
° r S a ns, or lungs, which have the power ol locomotion. 
. Tlie muscular system, as already stated, is almost always present 
the Echinodermata, but the organs of locomotion are very various, 
Principal being the membranous tubes usually termed feet, or 
a,ll lnilacra, which issue from the ambulacral apertures ; but besides 
the ravs themselves are movable, and in animals which are free 
to- J 
th, 
llj °ve from place to place these arc used for the purpose. Thus in 
le common star-fish the rays may be bent towards the upper or lower 
Sllr lace of the disk, so as to facilitate its advance either in water over 
small 
very 
7 ■ 
spaces or up the vertical face of rocks. These ambulacra are 
numerous, disposed in rows along the under surface of the rays ; 
f llf! In .1, aurantiaca there are two simple rows of feet attached to 
^ ra y, and the vesicular part is deeply cleft into two lobes ; while 
A' nibens (Eig. 105) there are two double rows on each ray, and 
ac |* ^°°t has one undivided vesicle. 
^acli of these ambulacra consists of two parts, an internal and 
llera lly vesicular portion placed within the body, and a tubular 
II r l0 n outside, projecting from the surface through an aperture in 
. 8 kin or s ] le ii ) tbe tube being closed at the extremity, and terminat- 
S m a sucker, usually in the form of a disk slightly depressed in the 
ri re - The feet are thus muscular fleshy cylinders, hollow in the 
re > and very extensible ; by means of them the animal draws it- 
^cle, which forces the fluid into the hollow tube, or, where the 
r esic l° is wanting, by projecting the fluid into the tube by a com- 
Ull icating vessel. The tubular part is thus distended and elongated, 
