THE CLASSIFICATION OF ANIMALS 49 



of a distinct science. It is termed Entomology, and it is 

 in this branch that the practical importance of zoological 

 science to the life of man has been most effectively demon- 

 strated. Arachnida are very few in numbers compared to 

 insects, but most of them are distinctly harmfnl to man, from 

 the scorpion with its stinging tail, which lies in wait for the 

 bare-footed inhabitant of the tropics, to the mite popularly 

 termed the harvest bug, which burrows under the skin of 

 the reaper's legs as he mows the corn, and causes painful 

 boils. The spider perhaps merits tolerance as a destroyer 

 of insects. 



Next to the great phylum of Arthropoda comes the phylum 

 of Mollusca, familiarly 

 known to all as shell-fish. \ 



This phylum includes also ^^ ^^ , , A v v _ 5 

 the octopus and cuttlefish, 

 and amongst the latter are 

 included some of the largest 

 animals living. Like the 

 Arthropoda, the Mollusca 

 are characterised by their 



cuticle; but whereas ^^r^J^i^S.^ 

 amongst Arthropoda the 

 cuticle envelops the whole 

 body like an armour, the 

 cuticle of Mollusca, termed 

 the shell, is produced only 



by a limited region of the skin termed the mantle. The 

 rest of the skin remains soft, is in most cases covered 

 with cilia, and is provided with numerous glandular cells 

 which produce mucus or slime. It is to this last cir- 

 cumstance that the group owes its name, for Mollusca is 

 derived from the Latin mottis, soft. The mantle or shell- 

 bearing region usually projects as a free flap, termed the 

 mantle-lobe or mantle-fold, from the surface of the body, 

 and the rest of the body can usually be withdrawn within the 

 embrace of the mantle and overlying shell, and so the animal 

 is protected against its enemies. In contrast with the limbs 

 of Arthropoda, the organ of locomotion of Mollusca is a thick 

 muscular mass on the under surface of the body, termed the 



as an example of the division of 

 Mollusca called Pelecypoda ; /, 

 foot ; m, mantle ; o, o 1 , two pos- 

 terior openings between joined 

 mantle-flaps ; ,, shell. 



