The Mednsoid Stage of a ScypJwzoan. 25 



enlarged gastric cavity, the peripheral boundary of which 

 extends as far as the circular muscle. Four clusters of ten- 

 tacle-like interradial gastral filaments, or phacelli, are to be 

 found encircling the deeper portion of the short oesophagus. 

 They mark the dividing line between the oesophagus and 

 the true gastric cavity. It is from the latter cavity, imme- 

 diately within the phacelli, that the reproductive sacs take 

 their origin. 



In injected specimens the chymiferous tubes or gastro- 

 canals can be followed, in their ramifications, through the 

 substance of the disc and into the marginal lobes. Four 

 main canals extend perradially and four interradially, finally 

 opening into enlarged terminal cavities, located between the 

 radial muscle bands and below and around the marginal 

 sense-organs. 



Alternating with the perradial and interradial canals are 

 eight adradial canals which expand into as many terminal 

 chambers, one above each cluster of tentacles. The central 

 cavity of each tentacle communicates with the terminal 

 adradial chamber. 



The Nervous System. Near the base of each mar- 

 ginal sense-organ ganglia have been found, though a mar- 

 ginal nerve-ring has not been discovered. 



