188 Mr. A. Hancock on the Anatomy 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 msertion. 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. Tt has 
already been pointed out that in these genera this set of muscles 
compensates for the want of the circle of setze 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 
setee alluded to, but in a very rudimentary state, and probably of 
little or no functional utility: consequently these muscles are 
still present, though, as might be expected, not so fully developed 
as in those genera entirely deprived of this appendage. 
We have now gone through the wholeeof the muscular appa- 
ratus for retraction and propulsion, and to verify the use of the 
various sets of muscles, we must once more observe the animal 
while issuing from the cell. The first symptom indicative of the 
polype’s inclination to come forth is the contraction of the parietal 
muscles, causing the tunic in certain places to leave the walls of 
the cell, par ticularly towards the lower portion ; on this the polype 
commences to move up the cell, and at the same instant the tube- 
retractors relaxing the inverted lips of the orifice begin to be 
evolved, and as the contraction of the parietal muscles goes on 
the polype advances upwards, and more and more of the tube is 
turned out, in the manner of the eversion of the horn of the com- 
mon snail; at length the membranous cup makes its appearance, 
not doubled upon itself, but im an erect position—the margin first, 
just as the circle of sete is exserted in Bowerbankia. The cup at 
first is laterally compressed, having been packed longitudinally 
in the axis of the tube: the tips of the tentacles now emerge 
through the centre of this cup, and as they pass upwards pressed 
together in a line side by side, its lateral folds give way, and by 
the time that the tentacular disc has reached the mouth of the 
cell, the cup is perfectly expanded. The muscles preventing the 
entire eversion of the tentacular sheath may now be seen in ac- 
tion near the upper extremity of the tube, holding back the mem- 
branous sheath and causing it to roll upon itself. The polype is 
now fairly above the mouth of the cell, and as the tentacles ex 
