A GENERAL REVIEW OF THE ANIMAL KINGDOM 147 



187. Phylum Porifera (pore-bearing). This group, to which 

 belong the sponges, is sometimes classed with the Ccelenterata. 

 While similar to them in habit the sponges are much less highly 

 organized and unified. Instead of a single mouth opening into 

 the digestive tract, sponges have many openings or pores 

 (whence the name Porifera) which are the beginnings of tubes 

 entering a central cloaca or sewer. This is in reality not a true 

 digestive tract. It communicates with the exterior by one or 

 more large passages. They are attached and usually form large 

 colonies by budding. 



1 88. Phylum Protozoa (first animals). All the preceding 

 phyla of animals consist, in the adult stage, of many cells among 

 which there is more or less differentiation. In all of them the 

 adult passes through stages in which the cells are arranged in at 

 least two layers (ectoderm and entoderm; see 55), from which 

 the tissue-masses arise. These animals are known as Metazoa. 

 In the remaining phylum the Protozoa the animals are 

 single cells, or at most, loose aggregations of similar cells. 

 They are the lowest of animals and are for the most part in- 

 visible to the naked eye. 



189. An Artificial Key to the Phyla of the Animal Kingdom. 



Many-celled animals METAZOA. 



With true coelom Coelomata. 



Possessing notochord (and often vertebral column), 



Phylum Chordata. 

 Possess functional gills. 



Throughout life Class Fishes. 



In embryonic life only (with a few exceptions), 



Class Amphibia. 

 Do not possess functional gills. 



Epidermal covering of scales Class Reptiles. 



Epidermal covering of feathers Class Birds. 



Epidermal covering of hair Class Mammals. 



Without notochord* Invertebrata. 



Bilaterally symmetrical (chiefly). 

 Body made up of segments. 



Paired appendages jointed Phylum Arthropoda. 



Paired appendages unjointed Phylum Annulata. _ 



Body unsegmented; without paired appendages. 

 With mantle often secreting shell, 



Phylum Mollusca. 

 No mantle Unsegmented Worms. 



