AFFINITIES. 103 



3. The form of the tentacular stage, i.e., 

 whether it be circular (Holobranchia) as in 

 the GYMNOL^EMATA, or like a horse-shoe 

 (Pterobranchia), as in the PHYLACTOL^MATA. 



Considerations 2 and 3 concern the 

 Ectoprocta. 



The Entoprocta are few, and of rather 

 doubtful position as regards the Polyzoa. In 

 them there is no Epistome, and the tentacle 

 stage is neither a complete circle nor thrown 

 out into arms. 



In some species (Loxosoma), there is a 

 pedal gland comparable to the peduncle in the 

 Brachiopoda. 



Affinities. The Polyzoa appear to be cut 

 off* by absent forms from very near ancestors. 

 Perhaps the nearest approach to their 

 structure is to be found in the ROTIFERA, which 

 are microscopic water animals, sometimes 

 single, sometimes compound, and either fixed 

 or free. At the oral end of the body there is 

 a ciliated disc, capable of withdrawal. They 

 have an alimentary canal and anus, a bladder 

 and water vascular system. There is also a 



