1(> KKVIKWS. 



se<>m to be of the liature of cilia, because they exhibit no motion. These minute 

 srt;v appear to be Mated on the 'peculiar body,' or, at all events, to be moved 

 with it, and the lattor, 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 setae 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 level of the cup, and are withdrawn into it as the mandible closes.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., Notamiu 

 burnaria, Buyula 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.' The prehension of living objects 

 by these organs has been repeatedly observed ; and, on one occasion, I have 

 witnessed the capture of a minute vermide, 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 maculafa^) 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 Vibracula 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 tentucula are pro- 

 truded. 



4 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 Vibracula 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 numy 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 morr directly with the intrinsic nature of the 



