TYPE G(ELENTEBA. 115 



depths of the ocean the simple forms which do not produce colonies are 

 frequently found. 



Relationships of the Anthozoa. — As has been pointed out, it seems prob- 

 able that the Anthozoa are to be traced back to a Scyphostoma-like polyp 

 lacking interradial funnels. No four-mesenteried form, however, is known, 

 a large gap existing between the Soyphostoma and the Alcyonaria, which 

 are probably the simplest Anthozoa known to us. The primitive Alcyonaria 

 were undoubtedly simple forms, and from them to the Edwardsise was not 

 a very great step. By t'he formation of four additional mesenteries the 

 Edwardsian condition became converted into the twelve-mesenteried con- 

 dition which forms the ground-form of the Protactinise, Zoantheee, and 

 Hexactiniee, the various stages seen in the Protactinise indicating the 

 manner in which the Hexactinian condition has been brought about. 

 The CerianthesB seem to be ofEsets from the Edwardsian condition, but it is 

 difficult in the present state of our knowledge to conjecture the affinities of 

 the Antipatharia. 



It is noticeable that the members of all the orders except the Hexac- 

 tiniee have a strictly bilateral arrangement and development of the mesen- 

 teries ; this arrangement becomes gradually modified, first, by the ten- 

 dency of the mesenteries to arrange themselves in pairs ; second, by the 

 formation of secondary mesenteries ; third, by a tendency for these to 

 appear in pairs ; fourth, by a tendency for such pairs to appear in all the 

 intervals between the primary pairs. Thus the Anthozoa are forms which 

 are gradually specializing away from the radial symmetry characteristic 

 of all Coelenterates towards a bilateral symmetry, and the more pronounced 

 radiality of the Hexactiniee is a secondary condition. 



SUBKINGDOM METAZOA. 

 TYPE GCELENTERA. 

 I. Subtype PORTFERA.— "With pores in the walls aud without nemato- 

 eysts. 



1. Order Cafcarea. —Skeleton calcareous. 



(a) Ascon type. Leucosolenia. 

 (h) Sy con type. Orantia. 



2. Order Cornacuspongiw. — Skeleton of spongiolin, usually with 



simple siliceous spicules. 



(a) With spicules ; fresh water. Spongilla, Ephydatia. 



(b) "Without spicules ; marine. Euspongia. 



3. Order Spiculispongiw.—Skeleton of uniaxial or tetraxial sili- 



ceous spicules. Sometimes entirely wanting, 

 (a) Skeleton wanting. Halisarca. 

 (6) Skeleton present. Cliona, Esperella. 



4. Order Hyalospongia. — Skeleton of 6-rayed siliceous spicules. 



Euplectella. 



