2 
INTRODUCTION. 
species being able to support life near, in or on the sea. Their position 
in the animal world is shown in the table :— 
Protozoa. 
Porifera (Sponges). 
Ccelenterata (Anemones, etc.). 
Ctenophora (Jelly-fish, etc.). 
Echinodermata (Sea-urchins and starfish). 
Vermes (Worms). 
POLYZOA. 
Arthropod a. —Crustacea (Lobsters, etc.) 
Prototracheata (Peripatus). 
Myriapoda (Centipedes and millipedes). 
Insecta (Insects). 
Arachnida (spiders, mites, scorpions, etc.). 
Mollusc a (Snails, etc.). 
Brachiopoda. 
Chordata. —Hemichordata. 
Tunicata. 
Cephalochordata. 
Craniata. Cyclostomata. 
Pisces (Fish). 
Amphibia (Frogs). 
Reptilia (Snakes, etc.). 
Aves (Birds). 
Mammalia (Mammals). 
Economically, the insects are the most important group of animals 
next to the Mammals, Birds and Fishes. Their activities affect man 
daily, either from the nature and extent of their injuries to economically 
valuable plants, or to domestic animals, or to wild animals, or to stored 
produce, or from their value in yielding useful products ; or from the part 
they play in the economy of nature, in fertilising flowers, in scaveng¬ 
ing and cleansing the earth, in rendering waste matter available as plant 
food, in preserving the condition of the soil and in furnishing food for 
birds and fishes. 
Instinct and Habit.— What is the life of an insect ? In what way 
can it be compared with our own or with the life, for instance, of any of 
