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THE EVOLUTION OF THE METAZOA 



Turbellaria. The two typical properties of this organ system in 

 Anthozoa, the ectodermal gullet and sarcosepta, had been inhe- 

 rited at least as primordia from their turbellarian ancestors. 

 This standpoint explains many facts which could not be under- 

 stood till now. Both the pharynx as well as the tendency to form 



Fig. 32. Digestive systems of the three cnidarian polyps (A, 

 anthopolyp, B, scyphopolyp, C, hydropolyp); above longitudinal 

 sections, below, crossections (after Remane, somewhat altered). 



variously shaped diverticula are properties that occur generally 

 in Turbellaria. The formation of a gullet is phylogenetically 

 even older than the tendency of the intestine to form diver- 

 ticula, because the former had been inherited by Turbellaria 

 from their protozoan ancestors, as we will try to prove later. 

 Among the Cnidaria we find a pharynx as an invagination 

 of the external body layer and of the muscles that surround 

 the oral opening only in the Anthozoa. Previously it was 

 quite generally believed that an ectodermal gullet was also 



