DR. A. FARRE ON THE STRUCTURE OF THE CILIOBRACHI ATE POLYPI. 40/ 
cilia may be occasionally detected. On the opposite side, generally, of the pharynx, 
may be seen a line (fig's. 8 and 9. a.) running down to the cardia, and if this part be 
observed for a short time it will be seen that the pharynx is repeatedly distended, as 
by a sudden act of insufflation, and that whenever this distention takes place the part 
bounded by the line becomes expanded but quickly returns to its former position. 
It is probable that there is here a muscular apparatus by which these sudden expan- 
sions of the pharynx are effected. When at rest this part has much the appearance 
of a tube, which is marked by rough cross lines, and wants the spotted character of 
the surrounding parts (fig. 9.). 
This sudden expansion of the parietes of the pharynx, which takes place at irre- 
gular intervals, appears to be connected with the act of respiration as well as of nu- 
trition ; for not only are the particles of food thus admitted more freely into the sac, 
but the water is more readily renewed and brought more effectually into contact 
with its inner surface. 
With a view of determining to what extent the flow of water into the pharynx took 
place, some particles of carmine were diffused through the fluid in which the animals 
were placed. As soon as the cilia commenced vibrating, the particles of carmine 
were put into rapid motion, (fig. 7-) being carried in a stream down the inner surface 
of each arm, the greater part passing out again between their bases ; while of the 
remainder part turned upwards again and issued from the centre of the expanded 
arms, (a course best seen when the arms were turned forward) and a few were 
carried through the mouth into the pharynx, where they were submitted to a rota- 
tory motion by the action of the cilia lining its upper part ; and after remaining there 
a short time some were swallowed, while the rest escaped at the mouth, and their 
place was supplied by others. From this experiment it did not appear that the flow 
of fluid into the pharynx was so free as might be expected, seeing that the mouth is 
almost constantly open ; for except during the act of expansion, by which the sac is 
suddenly filled with water, the parietes are so nearly in contact as to obliterate a 
large portion of its cavity: at every expansion, however, the greater part of the 
water must be renewed. 
The size of the particles which the animal swallows appears to be regulated con- 
jointly by the mouth and tentacula. The aperture within the tentacular ring, which 
forms the mouth of the pharynx, is not capable of distention like the mouth of Hydra ; 
for if this part were to be engaged in swallowing large prey, the whole tentacular 
apparatus would be thrown into disorder, and the regular flow of fluid to the pharynx 
interrupted. Whilst, therefore, the diameter of the mouth prevents the admission of 
the larger particles, the size of the smaller ones will be regulated by the spaces be- 
tween the tentacula, which, like a sieve, of a degree of fineness proportioned to the 
number of the arms and the consequent width of their intermediate spaces, would 
allow all the finest particles to drain away, and retain in their area only those of an 
intermediate size. These readily flowing into the pharynx become subject to a selec- 
