CRINOIDEA ; COMATULA; PENTACRINUS. 459 



to be principally by the action of these cilia, that food is brought 

 towards the mouth. Although the digestive cavity has two 

 orifices, it is not constructed upon the plan of that of the 

 Echinida. There Is no separate alimentary canal ; but only a 

 stomach like that of the Asterice, with a short tubular prolonga- 

 tion, of which the orifice projects between the mouth and the 

 side of the disk. (This projecting orifice, which is very evident 

 in the Encrinites, has been commonly mistaken for the mouth, 

 which is much less apparent.) The Comatula often attaches 

 itself to sea- weeds, or other floating bodies; and, bending its 

 long arms in various directions, it presents a very elegant appear- 

 ance. Sometimes it swims freely through the sea, by an undu- 

 lating movement of these appendages ; and sometimes it employs 

 a part of them for seizing its prey, whilst with the remainder it 

 clings to rocks, corals, or other firm supports. 



1017. Now if we imagine a Comatula turned with its mouth 

 upwards, and the opposite surface of the disk prolonged into a 

 five-sided stalk, the root of which should be attached to some 

 solid body, we shall have the form of the Pentacrinus. With 

 the animals of this tribe we are chiefly acquainted by their skele- 

 tons alone. Only two species are known to exist at the present 

 time. One of these, the Pentacrinus Europceus, is found in the 

 Bay of Cork ; the other, the Pentacrinus caput Medusae, in the 

 neighbourhood of the West India Islands. The former only has 

 been observed in its living state ; and it is so minute, that the 

 anatomical investigation of its structure is a matter of some 

 difficulty. It appears, however, to correspond in every particular, 

 except the attachment by a stem, with the Comatula ; and there 

 appears good reason to regard it as, in fact, the young state of 

 that animal. When arrived at its full growth, the disk and arms 

 quit the stem, and pass the remaining term of their existence in 

 a state of freedom. The Pentacrinus caput Medusce is a much 

 larger animal, and its skeleton presents a most beautiful and 

 regular structure. The disk and arms are formed like those of 

 the Comatula; the latter are very numerous, and thickly set 

 with the jointed lateral appendages. The stem is more than a 

 foot long, and is composed of a large number of pieces similar to 



