REVIEWS. 1 5 



conviction of the importance of a more close and attentive observation of, 

 and would suggest to our fellow-students carefully to examine, them, as they 

 undoubtedly merit the statements made by our author, not only as they ap- 

 pear in print, but also by the test of actual observation. Much still re- 

 mains to be done upon this subject, which, however, requires patient indus- 

 try, joined to many mdependeut/fobservations, before any theory, however 

 plausible, can be finally adopted. We annex the summary we refer to, 

 and we trust that it will cause some of our sea-side readers to commence 

 an accurate and uninterrupted series of observations on these puzzling ap- 

 pendages. 



u The organs in question are of two kinds the one forming a sort of pincers, and 

 the other consisting of a long, slender, moveable 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 Avicularian is here understood to be applicable, and the 

 latter are termed Vibracula. With the respect to the structure of these organs of 

 either class, it is sufficient to remark, that however diverse 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 the 

 motile portion the mandible; as I have termed it, in the one case, and the seta in 

 the other. 



*' The Avicularian, besides the moveable mandible, which varies extremely in form 

 and length, always has a more or less well-marked corresponding fixed beak the 

 opponent, as it were, of the mandible, and serving to constitute the organ an in- 

 strument of prehension. 



" This beak is necessarily absent in the Vibraculum, which appears to be merely 

 a defensive organ, or, perhaps, in some cases (as in the Selenraiadce}, having a loco- 

 motive function ; and its absence in cases when the moveable part of the organ is 

 detached, would serve to distinguish the one kind of organ from the other. It is to 

 be regretted, however, that, in the instance of fossil species, when such a character 

 would be of extreme value, this beak, which is, I believe, always constituted of a 

 horny or chitinous substance, is removed with all other vestiges of the animal tissues. 

 The presence of the beak also serves to determine, in some cases, the Avicularian 

 nature of the organ, when, as in several species of the Lepralia, the setose form of 

 the mandible might indicate that it would be more correctly referred to the Vibra- 

 cular type. 



u 1. As regards the Avicularia. 



" These organs, which appear first to have been noticed by Ellis, have been in- 

 vestigated and described by many subsequent authors, among whom are particularly 

 to be noticed Mr. Darwin, Dr. Van Beneden, the late Professor John Reid, and 

 especially Nordmann and Krohn. 



" In some observations upon the structure of the Polyzoary, and other points in 

 the economy of the Notamia bursaria, published in the Transactions of the Mi- 

 croscopical Society for 1847, I described more particularly the structure of the 

 curious and unique form presented by the Avicularian presented in that Polyzoan, 

 pointing out, I believe for the first time, that the muscles were divisible into two 

 distinct sets one for the closing, and the other for the opening of the mandible ; I 

 also indicated that the mandible and beak were constituted of a different substance 

 from the rest of the organs before referred to ; and that besides the two sets of 

 muscles, the cup contained a * peculiar body of unknown nature.' 



" I have, in addition, to remark, that since then it has occurred to me to notice a 

 circumstance hitherto overlooked, and which may eventually serve to throw some 

 light upon the ' peculiar body' contained in the cell, to which I adverted in my 

 observations upon Notamia. It was in that species also that I first noticed the fact, 

 that when the mandible is thrown back, or, in other words, when the Avicularian 

 is open, a slight prominence comes into view, covered with delicate setae, which do not 



