THE STUDY OF ZOOLOGY 25 



genus and species; thus the mountain salamander is known as 

 Desmognathus fuscus carolinensis and the closely related brook 

 salamander as the Desmognathus fuscus fuscus. These two forms 

 are varieties of the same species, and so far as one knows, are not 

 connected by intermediate forms at the present time. 



Animal Phyla. — The animal kingdom is composed of 17 

 animal phyla, of which the names of those commonly used in 

 laboratory study, with examples of each, are as follows: 



Protozoa, unicellular animals, microscopic in size such as Amoeba and 

 Paramecium. 



Porifera, sponges. 



Coelenterata, hydra, jelly fishes. 



Ctenophora, sea walnut, comb jelly. 



Platyhelminthes, flatworms, tapeworms. 



Nemathelminthes, roundworms or threadworms. 



Trochelminthes, rotifers. 



Annelida, segmented worms, such as the earthworm. 



Arthropoda, crayfish, crabs, insects, spiders. 



Mollusca, snails, clams, oysters. 



Echinodermata, starfishes, sea urchins. 



Chordata, animals with a notochord, of which the most important sub- 

 division is the Vertebrata, animals with a backbone. 



The classification of animals is considered in some detail in the 

 final chapter (XVIII), which should be consulted whenever a 

 new or unfamiliar animal is mentioned in the text. Since a very 

 definite part of the program of an introductory course in zoology 

 is a mastery of the fundamental facts of animal taxonomy, the 

 student is expected to learn the names of all the animal phyla and 

 their principal subdivisions and to acquire more detailed knowl- 

 edge of those phyla, of which examples are studied in the labora- 

 tory. This knowledge can best be acquired by a process of 

 gradual absorption, learning the important facts about a single 

 phylum, one at a time, until the entire system has been mastered. 



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