92 INTRODUCTION TO POLYZOA. 



The word Polyzoa signifies an association 

 of animals. The group are thus termed on 

 account of their habit of forming extensive 

 colonies, by a process of budding, such buds 

 being permanently retained in organic 

 connection. 



Form of Polypide. The Polypide, or 

 Zooid, as the individual Polyzoon is variously 

 termed, is minute, and may be generally 

 described as having a body more or less oval 

 in form, consisting mainly of a body-wall, and 

 an alimentary canal suspended within it. 

 With the exception of a few not altogether 

 undoubtful forms in Entoprocta, the polyzoa 

 are capable of withdrawing inwards one end 

 of the body, thus forming a kind of funnel, at 

 the bottom of which lies the mouth ; and 

 around it are arranged ciliated gill-tentacles. 

 These tentacles, when the retractile end of the 

 animal is thus withdrawn, lie within the 

 funnel-shaped depression, and it is therefore 

 known as the tentacle sheath. The mouth 

 leads into a tube which is a prolongation of 

 the funnel wall, and represents the oesophagus, 

 or commencement of the alimentary canal. 



