INTRODUCTION 



25 



Figure 8 shows by 

 this is modified from 



II. P 



a diagram one method of classification; 

 Lankester's " Treatise on Zoology," Part 



2. 



4. Phylum Ctenophora 

 3. Phylum Coelenterata 



t 



Enteroccela 



(Animals with single 

 body cavity, the 

 enteron) 



2. Phylum Porifera 



Parazoa 

 (Sponges) 



11. 

 10. 



9- 

 8. 



7- 



6. 



5- 



Phylum Chordata 

 Phylum Mollusca 

 Phylum Arthropoda 

 Phylum Annelida 

 Phylum Echinodermata 

 Phylum Nemathelminthes 

 Phylum Platyhelminthes 



t 



CCELOMOCCELA 



(Animals with two 

 body cavities, en- 

 teron and ccelom) 



Enterozoa 



(Primitively a dou- 

 ble-walled sac with 

 a single external 

 opening) 



Metazoa 



(Many-celled animals) 



1. Phylum Protozoa 

 (One-celled animals) 



Fig. 8. — Classification. Diagram showing one way of classifying animals. 



9. Zoology and its Subsciences 



Zoology is the science of animals, but the facts about animals 

 and the methods of studying them have become so numerous 

 that one man in his lifetime can master and become an authority 

 on only one, or at most a few phases of the subject. It has, 

 therefore, been found necessary and convenient to divide Zoology 

 into subsciences. The principal subsciences are named and very 

 briefly defined in Table II. 



