BRYOZOA, WITH DESCRIPTIONS OF NEW SPECIES. 389 
sufficient to perform the act of protrusion. From the movements 
of the alimentary canal, it is pretty evident that it has the power 
of straightening itself: but when quite straight, only a portion 
of the tentacles would be protruded beyond the cell; and here 
they would remain, for it is very clear that whether straight or 
bent, the alimentary canal will displace the same quantity of fluid, 
and that there would be no increase of pressure to force the ani- 
mal upwards. It is, at the moment, when the alimentary canal is 
being straightened that the parietal muscles come into play, and 
compel the animal to rise above the cell : these acts are perfectly 
simultaneous. The protrusion, therefore, of the polype, with a 
bent cesophagus and intestine is effected in the same manner as 
that in which these organs are straight; only that in the former 
it is accompanied with the straightening of the alimentary canal. 
The sixth and last set of muscles to be described, is for the 
purpose of preventing the entire eversion of the tentacular sheath. 
This set, Pl. V. figs. 1 7, r & 2 q, q, is the homologue of the 
strong radiating muscles in Plumatella and Fredericella ; but the 
fibres are much less numerous. In Paludicella they are only four 
in number, and take their origin from the inner surface of the 
cell, two in front immediately below where the tube joins the cell, 
and two behind in a line with the upper wall of the tube; hence 
the fibres are placed in front of, and behind the polype, and are 
inserted into opposite points of the tentacular sheath a little way 
below its summit, having on each side of them the two bundles 
of the tube-retractors. In the retracted state of the polype, these 
fibres are seen passing downwards towards their insertion. When 
the polype is protruded, these muscles cause the sheath to double 
upon itself, and thus retain a portion of it within the tube ; but 
not to the same extent as in Plumatella and Fredericella. It has 
already been pointed out that in these genera, this set of muscles 
compensates for the want of the circle of setee which surmounts 
the orifice in the marine species. In Paludicella, however, we 
have already seen that there is a wide, delicate, membranous cup, 
which rises from the inner surface of the tube, a little within the 
orifice. This cup is undoubtedly the homologue of the circle of 
sete alluded to, but ina very rudimentary state, and probably of 
