16 
REVIEWS. 
seem to be of the nature of cilia, because they exhibit no motion. These minute 
setae appear to be seated on the 4 peculiar body,’ or, at all events, to be moved 
with it, and the latter, again, seems to be so connected with the muscles by which 
the mandible is closed, or rather, perhaps, to be a membrane by which the open¬ 
ing of the cell is covered, when the mandible is thrown back, as to be protruded, 
simply by the throwing back of that process. The setce then project beyond the 
level of the cup, and are withdrawn into it as the mandible closes. I have noticed 
this arrangement, at present, only in three species of Polyzoa—viz., Notamia 
bursaria, Bugula plumosa , and B. avicularia. In Scrupocellaria scruposa , the 
only other species I have had sufficient opportunity of examining in a living state, 
I failed in detecting, and am, therefore, not prepared to state that it obtains 
universally; the setce might be supposed to constitute a tactile organ, the object 
of which would be to apprise the occlusor muscles of the contact of any minute 
floating object, upon which the mandible is then suddenly closed. 
44 With respect to the function of the Avicularia, several circumstances, indepen¬ 
dent of their conformation, conspire, I think, to show that they are probably 
organs of prehension. 
44 Their structure so obviously indicates an aptitude for prehension, that the sup¬ 
position of such being their function has long been entertained. The prehension 
of objects may be either for purposes of defence, or, more probably, for 
the procuring of food; for, as Dr. Johnson observes, ‘ although they are 
too short to hand the prey to the mouth, yet retained, in a certain position, 
and enfeebled or killed by the grasp, the currents set in motion by the ciliated 
tentacula may then carry it within reach. 7 The prehension of living objects 
by these organs has been repeatedly observed; and, on one occasion, I have 
witnessed the capture of a minute vermicle, by two of the Avicularia, simulta¬ 
neously, on opposite sides of a branch of Scrupocellaria scruposa, and its reten¬ 
tion by them for several days, notwithstanding the continuous and vigorous efforts 
of the victim to escape. 
“With respect to the Vibracula that they consist of a cup containing the muscular 
apparatus, and of a movable seta articulated to the cup, and which appears to be 
moved in the same way as the mandible of the Avicularia, this seta is, in most 
cases, simple and terrete ; and in others, as in the family Selenariadse, the seta is 
very variously and curiously formed—in some being bifid or trifid at the extremity ; 
and in one ( Selenaria maculata ) it is spirally contorted and minutely annulated, so 
as very closely to resemble the proboscis of a butterfly. 
44 As to the function of the Yibracula it would appear, in most instances, to be 
simply defensive. The seta may be observed in almost continual motion, sweeping 
slowly and carefully over the surface of the polyzoary, and removing what might 
be noxious to the general inhabitants of the cells when their tentacula are pro¬ 
truded. 
“Another circumstance, however, often to be observed with respect to these 
organs is this, that each presents inferiorly a perforation sometimes rounded, as in 
Scrupocellaria and Canda ; sometimes channelled, as in Caberea, which indicates 
the point of attachment of a radical root or fibre. But that this connection with 
a radical tube is not an essential attribute of the vibracular organ is sufficiently 
obvious from the circumstance, that those tubes are frequently found where no 
such organs exist; while, on the other hand, where there are Vibracula, the tubes 
invariably enter them, and not the cell itself. This is especially evident in the 
genus Canda . 
44 In the case of the Selenariadce , or Lunulites, I think it not improbable, as 
above remarked, that the Yibracula may be subservient to locomotion. This 
point would form a most interesting subject to those who may be so fortunate as to 
obtain these remarkable creatures in the living state. 
The Avicularian and Vibracular organs appear to be of very considerable im- ^ 
portance in a scientific point of view; and although, from our imperfect know¬ 
ledge of them—and, in fact, of many points in the economy and structure of 
the Polyzoa in general—the supposition can only be regarded as highly proble¬ 
matical—it seems not unlikely that their presence or absence, especially of the 
Avicularian, may be connected more directly with the intrinsic nature of the 
