INTRODUCTION 25 



Figure 8 shows by a diagram one method of classification; 

 this is modified from Lankester's " Treatise on Zoology," Part 



II, p. 2. 



ii. Phylum Chordata 



10. Phylum Mollusca 



9^ Phylum Arthropoda 



8. Phylum Annelida 



7. Phylum Echinodermata 



4. Phylum Ctenophora 6. Phylum Nemathelminthes 



3. Phylum Coslenterata 5. Phylum Platyhelminthes 



ENTEROCCELA 



(Animals with single 

 body cavity, the 

 enteron) 



2. Phylum Porifera 



I 



PARAZOA 

 (Sponges) 



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) 



I 



i. 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. 



