Calcispongige in the Animal Kingdom. 253 



In our sense the Acalephae coincide with the Nematopliora of 

 Huxley, and include as three classes the Hydromedusas, Cteno- 

 phora, and Corals (or Anthozoa). The denomination is the 

 more suitable, as, in fact, the urticating organs seem to form 

 the most constant distinction between the Sponges and 

 Acalephse. 



3. Above all, I reject the denomination (7«/6>i/erato, because 

 I conceive this group of animals in quite a different sense from 

 Leuckart. This author from the first regarded the central 

 cavity and its ramifications not as a stomachy but as a hocly- 

 cavity] and he has also recently (1869) expressly opposed the 

 notion " that the internal apparatus of cavities in them repre- 

 sents in its morphological significance the body-cavity of other 

 animals." I, on the contrary, share in the views of Gegen- 

 baur (1861),Noschin (1865), Semper (1867), and Kowalevsky 

 (1868), that the Coelenterata (both Acalephfe and Sponges) 

 2)0ssess no hody-cavity at all, and that their internal system of 

 cavities is rather homologous with the intestinal cavity of 

 other animals. This opinion appears to me to be phylogeneti- 

 cally of the greatest importance for the comprehension of the 

 homologies of the animal stem ; and it stands in the fullest 

 agreement with the germ-lamella theory. 



5. The Oerm-lamella Theory and the Genealogical Tree of the 

 Animal Kingdom. 



Among the phylogenetic questions which have been brought 

 into the foreground of philosophical zoology by Darwin's epoch- 

 making reform of the theory of descendence, one of the most 

 difficult and obscure, but also one of the most interesting and 

 important, is the question of the hlood-relationshij) of the types 

 or phyla, the great primary divisions of the animal kingdom, 

 which, since the time of Von Baer and Cuvier have passed as 

 entirely separate and independent unities. In 1866, in my 

 general phylogeny *, I made the first attempt to answer this 

 question, and indeed so far that I assumed the common deri- 

 vation of the whole animal kingdom from a single stock form, 

 but at the same time regarded the types of the Vertebrata, 

 Mollusca, Arthropoda, Echinodermata, and Vermes as narrower 

 genealogical unities, which were united only at the root. I 

 have also endeavoured to prove this connexion more clearly, 

 and to render it more precise in detail, by the demonstration of 

 intermediate forms, in my ' Natiirliche Schopfungsgeschichte ' 

 (1868, pi. 3 ; 3rd edit., 1872, p. 449). 



* Generell-e Morphologie, Bd. ii. pp. 408-417, pi. 1. 



