INTRODUCTION. IxXV 



thiuk^ be concluded that it is the concomitant of the 

 more highly specialized form. 



I may add that the avicularia in Notamia have very 

 much the shape and general appearance of zooecia reduced 

 in size, and are placed^ like the latter, in opposite pairs. 



We pass now to the articulated forms, in which the 

 zooecial type is completely masked, its elements being so 

 modified as to constitute an elaborate prehensile appen- 

 dage, charged with a special service in the interests of the 

 colony (Woodcut, fig. xxviii.). 



In the articulated avicularium the '' bird^s head " is suj)- 

 ported on a short peduncle with a basal joint, on which it 

 sways to and fro. The head is composed of two portions, 

 — a lower, which is more or less rounded above, and forms 

 the chamber for the muscles ( = the cavity of the zooecium) , 

 and an upper or anterior, which consists of a movable 

 mandible and a curved beak opposed to it. This anterior 

 portion is formed of horny material, whilst the chamber 

 itself is calcareous. The walls of the projecting upper 



Fig. xxxix. 



Eudimentary Polypide in Avicularium. 

 c. Cellular body. sc. Setiferous cup. s. Setce. rn. Membrane closing 



orifice. 



jaw, which terminates in the hooked beak, inclose an aper- 

 tui'C, over which stretches a delicate membrane, pierced 

 by a small circular orifice. This aperture represents the 



