98 INTRODUCTION TO POLYZOA. 



observed that the elements often come to 

 maturity at different periods. It is likewise 

 inferred that the embryo only escapes after 

 the break up of the Polypide. In Alcyonidium 

 there occurs an " intertentacular pore," and in 

 Pedicellina and Loxosoma there have been 

 discovered ciliated tubes (? nephridia) connect- 

 ing the body-cavity with the exterior, and 

 evidently subserving excretion. 



Ovicells in Cyclostotnata. In one 



group of the Polyzoa (CYCLOSTOMATA), the 

 Polypide cells become modified into special 

 chambers (Ovicells), for the rearing of the 

 embryos. 



Ovicells in Cheilostomata. In 



another group (Cheilostomata), there occurs 

 at the head of the Polypide cell an inflation of 

 the cell- wall, forming a recess of the body- 

 cavity, in which the embryos are lodged 

 during maturation. It is termed an Ovicell. 



The forms and markings of these Ovicells 

 are very good guides for specific determination. 



Operculum in Cheilostomata. In 



the same group of Polyzoa (Oheilostoinata), 

 the mouth of the Polypide cell is furnished 



