FIELD BOOK OF PONDS AND STREAMS 



The food tube of bryozoans is a U-shaped canal, with the 

 anus opening near the mouth, either just inside or just outside 

 of the circlet of tentacles (Fig. 103). Below the tentacles the 

 body is very flexible and provided with muscles by which the 



Fig. 103. — Individual animals of Plumatella: i, 

 lophophore with tentacles expanded; 2, with ten- 

 tacles retracted within the zooecium; 3, food tube; 

 4, anus; 5, developing statoblast. 



animals can pull themselves, tentacles and all, into their 

 shell-like coverings, the zooecia, or into surrounding jelly. 

 No one who has witnessed a sudden disappearance of these 

 animal gardens before his eyes can doubt its efficiency in 

 protecting them against nibbling enemies. 



The individual bryozoans which start a new colony in 

 spring are themselv^es produced either from sex cells, or from 

 winter buds called statoblasts (Fig. 103), which are very 

 similar to the gemmules of sponges. Like hydras the fresh 



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