OBSERVATIONS 



ON THE 



AV1CULARIAN AND VIBEACULAR ORGANS 



OF THE 



POLYZOA. 



IN the characters of the species of cheilostomatous Polyzoa 

 contained in the foregoing two Parts of this Catalogue, consider- 

 able use has been made of the avicularian and vibracular organs, 

 the possession of which appears, so far as I know, to be peculiar 

 to that Suborder. I have therefore thought that it might be 

 useful to subjoin a few observations on the subject of these 

 organs, for the purpose of indicating how far our knowledge of 

 them at present extends, and of directing attention more parti- 

 cularly to their value as affording diagnostic or systematic cha- 

 racters. Much of the following observations is taken from a 

 paper recently published in the Transactions of the Micro- 

 scopical Society, with which figures are given illustrative of the 

 subject. 



The organs in question are of two kinds, the one forming a 

 sort of pincers, and the other consisting of a long, slender, move- 

 able seta, and the muscles by which it is moved contained in a 

 special receptacle or cell. 



To the former set of organs, of whatever form, the term am- 

 cularium is here understood to be applicable, and the latter are 

 designated as vibracula. With respect to the structure of these 

 organs of either class it is sufficient to remark, that, however di- 

 verse their appearance may be, they are all constructed upon the 

 same general type, that is to say, the organ consists of a hollow 

 cup, containing two sets of muscles for the movements of its 



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