POL YZOA 



99 



The tentacles are numerous, and are united at their base 

 to form a funnel-like structure at the bottom of which is 

 the mouth. A careful 

 study of such Polyzoans 

 has revealed that within 

 each zooecium is a lining 

 of living cells, and within 

 this a body-cavity (a true 

 coelom) containing a U- 

 shaped alimentary canal, 

 the anus opening close to 

 the mouth of the zooecium 

 (cp. Bugula, Fig. 52). A 

 rudimentary nervous system 

 is present, but no vascular 

 system. In Flustra there 

 are no excretory organs, but 

 these occur in some Polyzoa. 

 Another very 



genus 



pida, but this Only OCCUrs FlG - 52.-The Bird's- Head Coralline (Du- 

 P J qulaaricvlaria}. Two zooids much mag- 



as encrustations, frequently nifiecL (From Parker and H aswell.) 



011 r UCUS. an> Anus ; owe, avicularia ; emb, an embryo ; 



MenibranipOTtl is another funic, funiculus ; mo, mouth ; stom, stomach ; 



which makes a *> ovary ; sp > spermary ' 



whitish lace-like encrustation on Laminaria. 

 In Bugula avicularia, the common Bird's- 

 Head Coralline, the colony has a tree -like 

 form, and may be several inches high. It 

 forms brownish or purple tufts on rocks or 

 pieces of wood in the sea. Bugula turlinata 

 has a spiral form (Fig. 53). 



In this genus, each zooecium has attached 

 to it a curious little body, very like a bird's 

 size. (From the head, called an " avicularium." The " beak " 

 (J,,Mdge Mural f ihi structure is constantly moving, the 

 History.) . J , . 



two parts oi it opening and shutting 



again with a snap. 



Rejuvena- A curious feature in the life-history of these 

 tion. Polyzoa is the way in which at times the central 



FIG. 53. fiwjula 

 1n r'nina.ta, a small 

 colony, natural 



