AVICULARIA 



483 



Having arrived at this point, the avicularia seem to lose all 

 sense of the propriety of remaining in the positions once occupied 

 by zooecia. They have become degraded to the rank of append- 

 ages of the zooecia, and as such they may occur in an astonishing 

 variety of positions. Sometimes one occurs on each zooecium in 

 the middle line, or asymmetrically, or even on the top of the 

 ovicell ; in other cases the 

 orifice is flanked by an avi- 

 cularium on each side (Fig. 

 239, B). Sometimes (Celle- 

 pora) the avicularia are of 

 more than one kind, some 

 being large and some small, 

 some having a pointed man- 

 dible and others a mandible 

 with a rounded spoon-like 

 end. 



In the cases so far con- 

 sidered, the body of the 

 avicularium is fixed. The 

 highest differentiation 

 acquired by these structures 

 occurs in cases like Bugula, 

 where they are borne on 

 flexible stalks, which may 

 even exceed the avicularia 

 in length. 1 



In Bugula turbinata (Fig. 

 240) each zooecium is pro- 

 vided with one of these 

 appendages, attached to the FIG. 240. j 

 base of the outer of the two lar i a ( a 



i'ii i 468. 



.spines which border its ori- 

 fice. The avicularia of the two edges of the flattened branch 

 are much larger than those of the more internal zooecia. The 

 upper jaw is strengthened by a kind of buttress, or thickening 

 of the ectocyst, which passes on each side across the avicularium 

 to the hinge-line of its mandible. The upper part of the beak 

 is strongly hooked, while the tip of the mandible bears a 

 1 "Challenger" Report, part xxx. 1884, pi. ix. 



turbinata, showing avicu- 



The fi ure "planed on P . 



