44 ZOOLOGY sect, i 



need not be described here, are referable to the phjdum Mollusca. 

 Other familiar animals are readily to be recognised as belonging to 

 one or other of these great phyla. A Prawn, a Crab, a Blue-bottle 

 Fly, a Spider, are all on the same general plan as the Lobster : they 

 are jointed animals with jointed limbs, and 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, and 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. A Dog, a Lizard, and a Fowl, 

 again, are obviously nearer the Fish : they all have a skull and 

 backbone, brain and spinal cord, and two pairs of limbs, and are 

 members of the great group Ghordata. 



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



I. Protozoa VII. Molluscoida 



II. Porifera VIII. Echinodermata 



III. Gcelenterata, IX. Annulata 



IV. Platyhelminthes X. Arthropoda 

 V. Nemathelminthes XL Mollusca 



VI. Trochelminthes XII. Ghordata 



But these do not comprise all known animals. There are a 

 number of smaller groups which are only very doubtfully to be 

 associated with one or other of the phyla ; and it is in some cases 

 chiefly to avoid multiplication of the latter that such groups are 

 not treated as independent. Such forms, until their places are 

 more definitely fixed, are best dealt with as appendices to the 

 phyla to which they appear most nearly related. 



