INTRODUCTION. 



In classifying the various objects around us, we divide tli<'ni 

 primarily into three great divisions, which are known as the 

 Animal, Vegetable, and Mineral Kingdoms. These are again 

 divided into smaller groups ; and one of the principal sections of 

 the Animal Kingdom is the sub-kingdom Annulom, or Artkidata, 

 so called from the animals included in it having bodies composed 

 of a number of joints or segments. Four classes are included in 

 the sub-kingdom Annulosa : Arachnida, including Spiders, Scor- 

 pions, and Mites ; Crustacea, including Crabs, Lobsters, Shrimps, 

 Woodlice, etc. ; Myriopoda, or Centipedes ; and Inseda, or Insects. 

 It is unnecessary to characterise the three first classes in detail, 

 but a few words will suffice to point out the chief characters by 

 which they differ from each other and from insects. The Arachnida 

 are destitute of the long jointed organs called antennae, so con- 

 spicuous in the other classes. They increase in size without under- 

 going any great changes of form. They are provided with eight 

 legs, and their body is composed of two principal parts only — the 

 cephalothorax and the abdomen. The Crustacea are provided with 

 two pairs of antennae, and a variable but moderate number of legs. 

 Their bodies are covered with hard shelly armour, and are not 

 divided into two or three well-defined sections, as in the Insects 

 and Arachnida, and they frequently pass through a very compli- 

 cated metamorphosis. The Myriopoda have long worm-like bodies, 

 one pair of antennae, and do not undergo a regular metamorphosis, 

 but as the)'^ grow, the number of segments of their bodies continues 

 to increase, and each segment being provided Avith a pair of legs, 

 the number of their legs also continues to increase until they have 

 reached their full growth. 



Insects differ from all the other groups in many important 

 characters. They are provided with one pair of antennae, six legs 

 only in the perfect state, their body is divided into head, thorax, 

 and abdomen, and they pass through four stages of existencf. 

 called respectively egg, larva, i)upa, and imago. These changes 



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