THE CLASSIFICATION OF ANIMALS 521 



protozoa are colonial, in which case the unit cells of the colony 

 are all potentially alike. There are four classes of protozoa. 



Class I — Rhizopoda (root-footed) . These cells have no fixed 

 form. The Amoeba proteus is one of the best known animals in 

 this class. The Amoeba histolitica causes a disease of the mouth. 

 Amoeba dysentericus causes summer complaint in children. 



Class II — Mastigophora. Move by one or more long, whip- 

 like threads of cytoplasm called flagella. Euglena viridis is an 

 example. 



Class III — Sporozoa. Parasitic Protozoa, usually lacking 

 motile organs or mouth. They reproduce by spores. Example : 

 Plasmodium malariae. 



Class IV — Infusoria. Animals which have many vibratile 

 processes (cilia), a cuticle, and fixed mouths and anal spots. 

 Paramecium caudatum, Vorticella. 



Phylum II — PORIFERA (Lat., poru^ — pore; ferre — bear). 

 Many-celled animals, so arranged as to form two layers of cells. 

 Their bodies are usually penetrated by numerous pores. The 

 cells of the body are supported by a skeleton of " spicules " or 

 material called spongii. There are three classes. 



Class I — Calcarea. Sponges with spicules composed of cal- 

 cium carbonate. Example : Grantia. 



Class II — Hexactinellida. Sponges with spicules of silica 

 triaxon in form. Glass sponges. Venus flower basket. 



Class III — Demospongia. Sponges with skeletons of spicules 

 of spongin or a combination of spongin and silicon. The bath 

 sponge is an example. 



Phylum III — COELENTERATA (Gr . koilus — hollow ; enteron 

 — intestine) . Composed of animals made of two layers of cells 

 invaginated to form a gastrula or internal cavity; they have a 

 mouth surrounded by tentacles and no anus. They are pro- 

 tected by stinging cells which also aid in killing prey. 



Class I — Hydrozoa. Single animals like Hydra fusca or colo- 



WH. FITZ. AD. BIO. — 34 



