iT2 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



has the function of an ingestive, and the other of an 

 egestive passage (Sedgwick). 



The walls of the digestive tract are not, as in the 

 Hydrozoa,in direct contact with those of the body ; the 



Fig. 55. Transverse Section of a Polyp of Ccelognrgia plumosa, 

 showing the long delicate cilia of the siphouoglyphe (si). (After 

 Hickson.) 



intermediate space is traversed by delicate plate-like 

 septa, some of which extend across the whole, and others 

 only partly project into the perigastric cavity (Fig. 

 54). The axial gastric space communicates at its 

 lower end with the compartments of the perigastric ; 

 and the septa project more or less inwards at this 

 point. Along the free edges of these septa there are 

 placed special filamentous structures, which are known 

 as the Mesenterial filaments, the name of mesen- 

 tery being applied to such septa as reach the walls of 

 the gastric tube. The only physiological experiments 

 yet made on those filaments are those of Krukenberg, 

 which demonstrate that these constituent cells act on 



