MODERN SYSTEMS. 293 



Since it can Le shown that Echinoderms arc, in a 

 general way, homologous in their structure with Acalephs 

 and Polypi, it must be admitted that these classes belong- 

 to one and the same great type, and that they are the 

 only representatives of the branch of Kadiata, assuming 

 of course that Bryozoa, Corallmse, Sponges, and all other 

 foreign admixtures, have been removed from among 

 Polyps. Now, it is this Cuvierian type of Eadiata, thus 

 freed of all its heterogeneous elements, which Leuckart 

 undertakes to divide into two branches, each of which he 

 considers coequal with Worms, Articulates, Mollusks, and 

 Vertebrates. He was undoubtedly led to this exaggera- 

 tion of the difference existing between Echinoderms on 

 one side, and Acalephs and Polypi on the other, by the 

 apparently greater resemblance of Medusae and Polypi, 1 

 and perhaps still more by the fact, that so many genuine 

 Acalephs, such as the Hydroids, including Tubularia, 

 Sertularia, Campanularia, etc., are still comprised by 

 most zoologists in the class of Polypi. 



But since the admirable investigations of J. Miiller 

 have made us familiar with the extraordinary metamor- 

 phosis of Echinoderms, and since the Ctenophorse and 

 the Siphonophorse have also been more carefully studied 

 by Grube, Leuckart, Kolliker, Vogt, Gegenbaur, and my- 

 self, the distance which seemed to separate Echinoderms 

 from Acalephs disappears entirely, for it is no exaggera- 

 tion to say, that, were the Pluteus-like forms of Echino- 

 derms not known to be an early stage in the transforma- 

 tion of Echinoderms, they would find as natural a place 

 among Ctenophorse, as the larvae of Insects among Worms. 

 I therefore maintain, that Polypi, Acalephs, and Echino- 



1 We see here clearly how the con- den the primary feature of branches, 

 sideration of anatomical differences their plan, and exalted a class to the 

 Avhich characterize classes hasoverrid- rank of a branch. 



