44 ZOOLOGY SECT. I 



spinal cord, and of two pairs of limbs (the paired fins) ; they belong 

 to the great vertebrate or backboned group the division Verte- 

 brafa of the phylum Chordala. The Lobsters, on the other hand, in 

 which these special vertebrate structures are absent, possess a body 

 which is enclosed in a hard jointed case, and a number of pairs of 

 limbs also enclosed in hard jointed cases and adapted to different 

 purposes in different parts of the body some being feelers, others 

 jaws, others legs : their general type of structure is that which 

 characterises the phylum Artliropoda. The Oysters, again, with 

 their hard calcareous shell secreted by a pair of special folds 

 of the skin constituting what is termed the mantle, and with a 

 special arrangement of the nervous system and other organs which 

 need not be described here, are referable to the phylum 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 Chordata. 



Altogether twelve phyla are to be recognised, viz. : 



I. Protozoa VII. Molluscoida 



II. Ponfera VIII. Echinodennata 



III. Ccelenterata IX. Annulaia 



IV. Platyhelminthes X. Arthropoda 

 V. NemathelmintJies XL Mollusca 



VI. Trochelminthes XII. Gliordata 



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. 



