PREVIOUS INTERPRETATIONS OF CNIDARIA 177 



When finally the idea has been given up, quite correctly, by 

 modern experts in Turbellaria to derive the Turbellaria from 

 the Cnidaria by way of Ctenophora, they have endeavoured, 

 together with von Graff, to go back to some common planuloid 

 ancestors and wait cautiously until the last word of the origin 

 of Cnidaria w^as said by the experts in Cnidaria. 



Here the question appears of what the anthozoan sarcosepta 

 actually are if we take into consideration their origin? What 

 is their function? How do they appear if compared with the 

 intestinal diverticula of Turbellaria, as well as of Ctenophora ? 

 We can get a clear idea if we study the morphogeny of 

 sarcosepta during ontogeny. Sarcosepta have developed due 

 to a longitudinal folding of the intestinal tube. We can say 

 that the first active step (similarly as in the formation 

 of the Anlagen of radial canals in the buds of Hydromedusae) 

 is made by the wall of the intestine by way of a stripe-like allo- 

 metry. During the next step the mesenchyme (mesogloea) grows 

 into the longitudinal folds in the interstices between these folds; 

 thus from the periphery and towards the centre, while at the 

 same time the growth of the longitudinal folds goes in the 

 opposite direction. We can therefore say that sarcosepta as 

 fully developed forms have been evolved due to a longitudinal 

 folding of the intestinal tube. This longitudinal folding is, from 

 the physiological standpoint, in reality the same thing as the 

 formation of diverticula by the intestine of Turbellaria; both 

 represent an increase of the internal digestive surface of the 

 entodermal epithelium and they both make possible the trans- 

 portation of the fluid food to the periphery of a body whose 

 size has been increased. A connective tissue (mesohyl) grows 

 between these diverticula and the longitudinal folds; gonads 

 and muscular fibres are later transplaced into it. 



At the first glance it does not seem to be important whether 

 in connection with the formation of sarcosepta we speak about 

 longitudinal folds, or about an ingrowth of septa. This diffe- 

 rence, however, is fundamental. It is the effect only, the final 

 static state, which are similar. 



