10 A SYNOPSIS OF ANIMAL CLASSIFICATION. 



Sub -order 2. Oc/ocoraZ/cs .... Mesenteries and tentacles always 



eight; coral consists of a horny 

 axis about which is built a polypa- 

 rium containing calcareous spicules 

 called sklerites. 



Renilla, Corallium. 



Order 2. ScYPHO-MEDUsa: Large medusae without velum, 



which are produced by minute 

 polyps of the scyphula type. This 

 order corresponds to that of the 

 Hydro-meduscB above, although here 

 the medusa form is by far the most 

 in evidence. Cyanea, Aurelia. 



Supplementary class : Planuloidea. Minute endoparasites, with- 

 out mouth or intestinal lumen, resembling the Planula larva of Cnidarian 

 polyps. There are two groups : the DicyemidcB^ found in the nephridia 

 of Cephalopods, and the Orthonectida, in Ophiuridea, Turbellaria, and 

 Nemertea. They have been considered as " Mesozoa," intermediate 

 between Protozoa and Metazoa, but are more probably Cnidaria, reduced 

 by parasitism. 



Sub-type II. CTENOPHORA. 



Floating pelagic forms, transparent and gelatinous, with eight 

 rows of swimming-paddles. Structure a modified radiate or doubly 

 bilateral one. No nettle-cells, but somewhat similar organs, and 

 adhesive cells. 



Class I. TENTACULATA With two long prehensile thread- 

 like tentacles. x Pleurobrachia. 

 Class II. NUDA Tentacles wanting. >t.Beroe. 



Sub-type III. PORIFERA. 



The typical members of this group are shaped like polyps with- 

 out tentacles, but with the lateral walls perforated by numerous 

 incurrent pores and with a large excurrent orifice, the osculum, at 

 the top. They possess between ectoderm and endoderm a mass of 

 cells, the mesenchyme, containing spicules or a network of horn- 

 threads. The more modified forms often grow into masses, the 

 individuals of which cannot be definitely distinguished. 



