186 Mr. A. Hancock on the Anatomy of the 
satisfactory to see whether a similar apparatus for closing the 
orifice could be found in the marine species, I examined specimens 
of Bowerbankia, and had the satisfaction of detecting sphincter 
muscles in the same situations. At the point of insertion of the 
inferior tube-retractors—according to Dr. Farre of the upper set 
of opercular muscles—the circular fibres are very distinct and nu- 
merous, forming a large portion of the inverted tube into a broad 
sphincter. These fibres are so conspicuous that it seems strange 
how they could have escaped the notice of so close and accurate 
an observer as Dr. Farre. It is possible enough, however, that 
they might be less developed in the species examined by him*. 
The sphincter at the point of insertion of the superior tube-re- 
tractors 1s not readily observed ; but when the polype is exserted 
there can be no doubt of its existence. 
The fifth set of muscles, figs. 1 & 5 ¢, h, isin connexion with the 
tunic or lining membrane of the cell, and is precisely similar to 
the parietal muscles described by Dr. Farre in the marine spe- 
cies. This set is formed of short, transverse belts, arranged in 
pairs, considerably apart from each other, which are to be found 
almost from end to end of the cell, but most conspicuously to- 
wards the lower extremity. There appears to be two sets of these 
fibres, one down the back, the other down the front of the cell ; 
but I could not arrive at any very satisfactory conclusion respect- 
ing their arrangement, neither could I determine their exact re- 
lationship to the tunic,—whether they are attached to it by their 
extremities only as supposed by Dr. Farre, or connected with it 
throughout their entire length. Professor Allman appears to be 
of the latter opinion, and certainly I saw nothing in confirmation 
of that expressed by Dr. Farre; though I am not sure that the 
extremities are not attached to the cell-walls, thus giving to these 
muscular belts fixed points of action. Howsoever this may be, 
these parietal muscles undoubtedly have the power of contracting 
the tunic, and so lessening the space within which the polype is 
confined ; the contained fluid is made to press on the surface of 
the polype, constraining it to pass upwards, and thus to effect its 
* In the species examined by Dr. Farre and named by him Bowerbankia 
densa, the tube-retractors have a “‘triradiate arrangement,” and consequently 
the orifice is puckered mto three folds when the polype is retracted. The 
species referred to in the text we have seen has four such folds—the tube- 
retractors being divided into as many bundles. ‘The circle of tentacles also 
assumes a different form in the two species: in that examined by me the 
tentacles rise from the disc im a straight, slightly diverging lme, and arch 
considerably outwards at the tips. In Dr. Farre’s species they arch out- 
wards immediately above the disc, and are very little recurved at the tips. 
It is therefore pretty evident that there are two species, and that B. densa 
should not be merged in B. imbricata, which is most probably the form that 
I have seen. . 
