STRUCTURAL RELATIONSHIP 313 



Class II. Infusoria. Unicellular organ- 

 isms provided with cilia or 

 flagella and having a localized 

 oral orifice. Multiply by bi- 

 nary fission. 



Class III. Sporozoa. Protoplasmic or- 

 ganism usually naked without 

 an oral orifice. Multiply by 

 dividing into many small 

 spores. 

 Division II. Metazoa. Multicellular animals. 



A. Without true ccelomic cavity Radially symmet- 

 rical. 



1. Without a notochord Invertebrata. 

 Phylu m Porifera . 



The sponges. Characterized by many 

 incurrent openings and only one excur- 

 rent opening. Axially symmetric. Sexu- 

 ally reproductive. 



Class I. Calcarea. Skeleton of cal- 

 careous spicules. 



Class II. Non-calcarea. Skeleton of 

 siliceous spicules and horny 

 fibres. 

 Phylum Ccelenterata. 



The jelly-fishes. Characterized by a single 

 mouth which also functionates as an 

 anus. Possess stinging or nettling 

 cells. 



Class I. Hydrozoa. 

 Class II. Scyphozoa. 

 Class III. Actinozoa. 

 Class IV. Ctenophora. 



B. With a true coelomic cavity Radially symmet- 

 rical. 



Phylum Echinodermata. 



The star-fishes, sea-urchins, sea-cucum- 

 bers, etc. 



