76 THE EVOLUTION OF THE METAZOA 



2oa-Scypho2oa-Antho2oa which has seemed to indicate a 

 progressive development. Frequently the latter two classes have 

 been united under the name Scyphozoa; for a long time it was 

 believed that both Anthozoa and Scyphozoa have an ectodermal 

 gullet (pharyx). It is worth mentioning that Haeckel himself 

 was partly irresolute whether the border line between Coelente- 

 rata and the more highly developed Coelomata should be 

 placed between Ctenophora and the lower Turbellaria, or some- 

 what higher so that Turbellaria could be included among 

 Coelenterata; it was clear that there was a relationship between 

 Ctenophora (particularly those that lived on the sea bottom) 

 and Turbellaria whose structure seems to be quite close to the 

 structure of the former— and for this reason these lower 

 "worms" could not be genuine Coelomata. On the other hand 

 such an extension of the sphere of Coelenterata could lead to 

 a muddle and to a system which it would be difficult to survey. 

 Carl Borner (1923) later proposed to associate Platyhel- 

 minthes and Acanthocephala more closely with Coelenterata. 

 Still, some changes were proposed in spite of the fact 

 that this part of the natural system of zoology appeared 

 very stable and that it had been generally accepted. T. H. 

 Huxley (1875) already expressed his doubts that there was 

 a close relationship between Spongiae and other Coelenterata, 

 and generally to Metazoa. It was Sollas (1884) who succeeded 

 in transforming this doubt into a fact, into a truth; he made 

 a definite separation of Spongiae, asParazoa, from Eumeta- 

 zoa as the genuine Metazoa. This radical step was well 

 supported by numerous and fundamental differences that 

 occur both in the structures and in the ways of life of 

 Spongiae and of other Metazoa. Even greater differences 

 have later been observed in connection with their onto- 

 genies. Delage tried to emphasize this difference when he in- 

 vented the name Enantiozoa for Spongiae, i.e. Spongiae are 

 Metazoa in whose ontogenies the layers of their bodies become 

 inverted: that layer of cells, which in an embryo or in a larva 

 occurs in their external or anterior parts, develops into the 



