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. 

 Anothervery 



PoSa. ^^""il^^ fo™ is 



Flustrella his- 



pida, but this only occurs Fig. 52.— The Bird'sHead Coralline (i3»- 

 , ,. J. ., gulaavicularia). Tv/ozooids much mag- 



as encrustations, frequently ^jfl.j (Fiom Parker and Haswell.) 



OIU UCUS. jj„^ Anus; ai-ic, avicuiaria; emb, an embryo; 



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

 genus which makes a »". ovary ; .p, 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 turUnaia 

 has a spiral form (Fig. 53). 

 Fig. 53. —/j «,-/(( a j ^j^- „gjjyg gg^^jj zooecium has attached 



turbinata, a small . . ,. , , , ,., i . i, 



colony, natural to it a cunous little body, very like a birds 



size. (From (he head, called an ^' avicularium." The " beak " 



Srf r '^'"'"'"^ of *^'^ structure is constantly moving, the 



two parts of it opening and shutting 



again with a snap. 



Eejuvena- ^ curious feature in the life-history of these 



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



