MUSCULAR SYSTEM. 
as it were the limbs of Crustaceans and other 
 Articulata. 
_ The study of the muscular system in the 
extensive class Ecurnopecmata, the last of 
the nematoneurose division of the animal world, 
is invested with considerable interest on account 
of the very different kinds of locomotive appa- 
ratus that successively make their appearance ; 
for as the outward form of these elaborately con- 
_ structed creatures changes through all the phases 
represented by the Encrinite, the Sturfishes, 
the Echinus, the Holothuria, and the worm- 
like Siponculus, the muscles successively assume 
a different arrangement. 
The Encrinite in its outward form might be 
_ mistaken for a polyp, the jointed calcareous 
“stem whereby it is fixed to the rock, the body 
‘and rays around the mouth, as well as the 
appendages to the stem, being all in their essen- 
al structure exactly comparable to those cor- 
_tieal polyps, that have an internal jointed cal- 
areous basis of support. The numerous 
‘pieces that compose the skeleton of the Encri- 
nite are all invested with a living contractile 
crust, whereby, in fact, they were secreted, 
d which forms the bond that connects them 
her. The living crust that covers the 
nerinite can scarcely, indeed, as yet be looked 
90n as being muscular, so soft and acrite 
does its composition appear to be; nevertheless 
in these Echinoderms it seems to be the only 
oving power employed, and by its slow con- 
actions bends the arms, or rays, or stem in 
given direction. 
_ In the long-armed Starfishes, such as the 
“Comatule, Gorgonocephali, and Ophiuri, the 
slender and flexible rays around the body are 
1 like manner covered with a living contracting 
, more dense and coriaceous than that of 
Encrinite, but still presenting very dubious 
earances of muscular fibre, whereby the 
ovements of the rays are effected. The rays 
emselves constitute the instruments of pro- 
sion, and by their aid these Polyp-like 
ures crawl at the bottom of the sea, or by 
itwining them around the sea-weed that covers 
the rocks climb in search of food. 
In Asterias and kindred forms the exterior 
of the hody is still encrusted with the same 
contractile covering, and can be bent to a 
certain extent; but in these short-armed Star- 
es the rays have become so short and devo.d 
f flexibility that they can no longer be useful 
the purposes of locomotion: an additional 
cular apparatus is therefore now conferred 
the extraordinary system of protrusible 
sers, that become the chief agents in walk- 
}, Or in seizing prey. 
_ As we advance from the Asteride we find 
the rays at length totally disappear: the 
y assumes a pentagonal form ( Pulmipes ), 
en circular ( Scutella ), and at last is enclosed 
ee ovoid or globular shell, as in Echinus, 
_ Cidaris, &c. In these spherical Echinoderms 
the external soft and living crust that still 
covers the exterior of the shell presents obvious 
claims to muscularity, more especially where 
‘it passes on to the articulated spines that are 
‘attached to the surface of the shell and now 
L 
tx 
537 
become the principal means of prozression. 
The suckers, however, that formed the only 
locomotive organs in the Asteride still are met 
with in the Echinide,—these and the spines 
constituting an apparatus for locomotion, which, 
for its complexity, is unparalleled in the ani- 
mal creation. In the Echinide, moreover, a 
strangely constructed set of dental organs are 
developed, and for these likewise special muscles 
are appointed, for a description of which the 
reader is referred elsewhere. (See Ecuino- 
DERMATA.) 
In the Holothuride the shell of the Echinus 
is no longer secreted, and the living integument 
itself constitutes the whole parietes of the body, 
which now becomes quite soft and flexible, 
clearly commencing that transition which is to 
connect the Echinodermata with the Annulose 
division of the animal kingdom. The suckers 
of the last family are, however, still persistent 
and form the principal means of moving from 
place to place. The texture of the fleshy skin 
of the [olothuria is dense and coriaceous, and 
strong bands of muscular fibre arranged in five 
divisions pass in a longitudinal direction, from 
one end of the body to the other, between 
which circular and transverse fasciculi are dis- 
tinctly perceptible. Imbedded in the muscular 
walls that enclose the visceral sac of the Holo- 
thuride, delicate nervous filaments are to be de- 
tected passing along the body froraend to end, and 
most probably these are connected together by 
a circular filament surrounding the esophagus. 
Ganglia, if they exist at all, have, from their 
minute size, hitherto esciped observation; and, 
as might be expected from such a condition of 
the nervous system, the muscular contractions 
of the fibrous integument, although associated 
through the medium of the nerves, and con- 
sequently far stronger and more energetic than in 
the lower asteroid Echinoderms, are still almost 
entirely uncontrolled by the influence of volition ; 
nay, so remarkably is this the case, that in 
most species of Holothuria, npon the applica- 
tion of the slightest stimulus to the exterior of 
the body, or even by simply taking them out 
of the water in which they live, such violent 
and general contraction; of the whole integu- 
ment are excited that the intestines and other 
viscera are forced extensively through the anal 
orifice, and it is almost impossible for the 
anatomist to procure a specimen of these crea- 
tures without finding it more or ‘less spoiled 
from this circumstance. 
Lastly, in the Siponculi the vermiform ap- 
pearance is completely established, the longi- 
tudinal and circular muscles that bound the 
visceral cavity are strongly and distinctly deve- 
loped, the complicated apparatus of foot-like 
suckers has disappeared, minute ganglia are 
visible towards the anterior end of the body, 
and we arrive at the annulose condition, that 
characterizes the next great division of the 
animal creation, which now offers itself to our 
contemplation. 
Homocancurata (Owen).—The third great 
natural group of living beings consists of crea- 
tures having the exterior of their bodies divided 
into rings or segments arranged behind each 
