106 



As to the function of the vibracula., it would appear in most 

 cases 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 delicate inhabitants of the cells when their tentacula are 

 protruded. 



Another circumstance, however, often to be observed with re- 

 spect to these organs, is this, that each presents inferiorly a 

 perforation sometimes rounded, as in Scruppcellaria and Canda, 

 sometimes channelled as in Caberea, which indicates the point of. 

 attachment of a radical tube or fibre. But that this connexion 

 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 when no such organs exist ; whilst 

 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. 



In the case of the Selenariadce or Lunulites, I think it not 

 improbable, as above remarked, that the vibracula may be sub- 

 servient to locomotion. This point and others would form a 

 most interesting subject of observation to those who may be for- 

 tunate enough to obtain these remarkable creatures in the living 

 state. 



The avicularian and vibracular organs appear to be of very 

 considerable importance in a systematic point of view; and 

 although from our imperfect knowledge 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 problema- 

 tical, it seems not unlikely that their presence or absence, espe- 

 cially of the avicularium, may be connected more directly 

 with the intrinsic nature of the species upon which they are 

 found, than has hitherto been supposed. It may, for instance, 

 be the case that those furnished with these offensive weapons 

 live upon a kind of food different from that of the others, who do 

 not require such an aid in the capture or weakening of their prey. 

 The Polyzoa may, perhaps, thus be divided into vegetable and 

 animal feeders ; or into feeders upon dead, and those which sub- 

 sist upon living organisms. One thing, however, may be affirmed, 

 that these organs afford, in many cases, excellent and available 

 systematic characters, of which application of them the preceding 

 Catalogue will afford abundant evidence; with respect to this 

 part of the subject it will therefore be unnecessary here to add 

 more than a few words. 



Of the two sets of organs, the avicularia are found by far 

 the most extensively; existing in fact in the majority of 

 genera constituting the cheilostomatous Polyzoa. In employing 



