406 DR. A. FARRE ON THE STRUCTURE OF THE CILIOBRACHI ATE POLYPI. 
flexible. When expanded they are frequently seen to roll up closely upon themselves, 
(fig. 18.) even down to their base, the revolution taking place either inwardly or 
outwardly, and in one or more arms at the same time. Their full expansion affords a 
more perfect campanulate form than is usually met with in this class, each of the 
arms having a slight curve outwards towards its extremity, which gives to the whole a 
very elegant appearance. It is remarkable that in some specimens the arms are 
much shorter on one side of the body than on the other. In many positions this is 
not very striking, as it might be attributed to an appearance of fore-shortening of 
that side which happens to be turned towards the observer, (fig. 17.) but when viewed 
laterally this character is very obvious (fig. 16.). The arms when viewed with an 
amplifying power of 200 linear are seen to be tubular throughout, (fig. 19. a.), and to 
have an aperture at each extremity. The aperture at the apex is extremely small, and 
in a lateral view sometimes appears like a slight notch at the extremity of the arm. 
The apertures at the base are seen more plainly, and are situated in the centre of the 
tentacular ring, one corresponding with the base of each arm (fig. 8.). I have also 
sometimes observed what would seem to be a fine canal, running round in the sub- 
stance of the ring, and apparently uniting the tentacular canals (fig. 10.). It would 
be exceedingly interesting to ascertain with what parts these tentacular canals com- 
municate. As the tentacles appear to be respiratory as well as prehensile organs, it 
is most probable that the canals by which they are permeated are for the purpose of 
allowing a circulation of fluid through them; but from the minuteness of the parts and 
the agitation of the surrounding medium by the rapid action of their cilia, it would 
be a matter of great nicety to detect such currents though they should exist. 
The action of the tentacular cilia appears entirely under the control of the animal, 
and they are sometimes seen completely at rest. If, however, a portion of one of the 
arms be cut off, the action of the cilia continues as vigorous as before, and the isolated 
part is carried about in the field of the microscope. When the animal is dead, these 
cilia are seen to be longer and considerably more numerous than they appeared to be 
when in action (fig. 19. a.). As the parts gradually perish the cilia disappear, and 
the surface of the arms becomes covered with a granular matter and the part shrinks 
to a mere thread (fig. 19. h and c.). 
The ring upon which the tentacles are set is well marked, and terminates on its inner 
circumference by a sharp edge projecting to form the mouth of the pharynx. It is 
probable that this tentacular ring never contracts except to bring the base of the 
tentacles together. But whilst it remains fixed so as not to alter the arrangement of 
the arms, the closing of the mouth of the pharynx is effected by the constriction of 
the parts immediately below it, which there appear as if they had been bound round 
with a ligature (fig. 8. d.). 
The pharynx (figs. 7? 8 and 9.) is very short in this species, and its parietes are 
covered by the peculiar spots already noticed, except in the triangular space at the 
upper part (fig. 9. c.) which is entirely free from them, and where a vibration of 
