PREVIOUS INTERPRETATIONS OF CNIDARIA 



143 



tunction considerably reduced as is particularly true for types 

 whose bodies are covered with a cuticle. The real excretory 

 function is always taken over by other organs or tissues 

 because this function remains unavoidably necessary due to 

 the metabolism of the animals, regardless of the w^ay in which 

 these animals feed. On one hand we can see nephrocytes(mesohyl 



Fig. 24. "Ciliate rosette" of the ctenophore species Coeloplana sp. 

 (after Komai), 



cells), i.e. cells of the same origin as protonephridial cells, and 

 on the other hand the intestinal cells, take over the function 

 of the lost protonephridia. This is also true for Cnidaria: the 

 second type of substitution is especially characteristic of the 

 rapidly moving medusae which have developed, as has already 

 been mentioned, excretory pores at ring canals as special 

 auxiliary organs. 



Finally we must not forget that it was aeons ago that 

 Cnidaria (as the first Eumetazoa to have adopted the sessile 

 way of life) were separated from Turbellaria. There has 

 therefore been plenty of time available for the reduction and 



