II THE METAZOA 75 



animals are readily to be recognised as belonging to one or 

 other of these great phyla. A prawn, a crab, a bluebottle 

 fly, a spider, are all on the same general plan as the 

 lobster : they are jointed animals with jointed limbs, and 

 they have the internal organs occupying similar positions 

 with relation to one another. They are all members of the 

 phylum Arthropoda. Again, a mussel, a snail, a squid, are 

 all to be set side by side with the oyster as conforming 

 to the same general type of structure ; they are all members 

 of the phylum Mollusca. Finally a dog, a lizard, a fowl, are 

 obviously nearer the fish : they all have skull and backbone, 

 brain and spinal cord, and two pairs of limbs ; they are all 

 members of the great group Chordata. 



Altogether twelve phyla are to be recognised, viz. : — 



I. Protozoa VII. Molluscoida 



II. Porifera VIII. Echinodcrmata 



III. Cxlenterata IX. Anmdata 



IV. Platyhelminth.es X. Arthropoda 

 V. Nemathcl mi utiles XI. Mollusca 



VI. Trochclminthes XII. Chordata 



