Fig. 20.—Hypohythhis calycodes. G, nerve garglion ; H, 

 heart ; M, the position of the atriopore. The large open- 

 ing on the upper side is the mouth. (From a drawing by 

 Professor Moseley in Herdman"s ' Tunicata of the "Chal- 

 lenger " Expedition.') 

 11 



