STRUCTURE OF AVICULARIUM. 437 



by a lively Bryozoic polyp, resembling in all essen- 

 tial particulars those described in the preceding 

 chapters. 



The Bugula avicularia, however, has received its 

 specific name from the presence of numerous remark- 

 able organic bodies (avicularia) that cannot fail to 

 attract the notice of all observers. The position and 

 nature of these strange objects, indeed, together with 

 the peculiar and unaccountable motions which they 

 exhibit, have proved a source of much embarrassment 

 to every one who has attempted their description. 



The " avicularium " presents the strongest resem- 

 blance, as its name would indicate, to a bird's head in 

 extreme miniature; nor is the comparison much 

 impaired, even when it is examined by powerful 

 magnifiers. It is always seated on the outside and 

 about the middle of a cell; and should the branch 

 of the Zoophyte be composed of a longitudinal series 

 of parallel cells, it is borne either alternately on 

 each margin of the branch, or on one margin only. 

 When examined with a lens, it seems to consist of 

 three distinct principal organs : first, a basis founded 

 on, and incorporated with, the cell ; next, a head con- 

 nected with the basis ; and in the third place, a lower 

 mandible, which exhibits the most lively movements. 

 In quiescence, the whole is like the head of a bird 

 with the bill closed ; but when in activity, the lower 

 mandible opening folds back with a very wide gape 

 (PI. VII. fig. 10). Another joint connects the head 

 with the basis, whereon the neck moves as in a 

 socket. The bill opens and closes frequently, as if 

 for the purpose of swallowing some extraneous matter 



