105 



to be of the nature of cilia, because they exhibit no motion. 

 These minute seta appear to be seated on the " 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 a membrane by which the opening 

 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 setae then project beyond the level of the cup, and are withdrawn 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. Notamia bur- 

 saria, Buaula plumosa, and jB. avicularia. In Scrupocellaria 

 scruposa, the only other species that I have had a sufficient op- 

 portunity of examining in the living state, I failed in detecting 

 it, and am therefore not prepared to assert that it obtains uni- 

 versally. The setcs 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. 



With respect to the function of the avicularia, several circum- 

 stances, independent of their conformation, conspire I think to 

 show that they are probably organs of prehension. 



Their structure so obviously indicates an aptitude for prehen- 

 sion, that the supposition of such being their function has long 

 been entertained. This prehension of objects may be either for 

 the purposes of defence, or more probably for the procuring of 

 food, for, as Dr. Johnston 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 witnessed the capture of a mi- 

 nute vermicule, by two of the avicularia, simultaneously, on op- 

 posite sides of a branch of Scrupocellaria scruposa, and its re- 

 tention by them for several days, notwithstanding the continued 

 and vigorous efforts of the victim to escape. 



With respect to the vibracula, 1 would merely observe, that 

 they consist of a cup containing the muscular apparatus, and of 

 a moveable 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 terete ; whilst in others, as 

 for instance generally in the genus Caberea, it is toothed on one 

 side ; and in others, as in the family Selenariadce, the seta is very 

 variously and curiously formed ; in some being bifid or trifid at 

 the extremity ; and in one, Selenaria maculata (PL CXVIL), it 

 is spirally contorted and minutely annulated, so as very closely 

 to resemble the proboscis of a butterfly. 



