CHAPTER XXm 



OTSECTA, A CLASS OF ARTHROPODS 



Vocabulary 



Trachea, a breathing tube, admitting air to the tissues. Plural: 

 tracheae. 



Chitin, a horn-like, elastic substance found in the external skeletons 

 of insects and other arthropods, pronounced "kite-in." 



Accessory, additional or assistant organs. 



Palpus, feeler or sense organ attached to the mouth parts of in- 

 sects, etc. Plural: palpi. 



Spiracles, external openings of the tracheae, used in breathing. 



Ganglion, a mass of nerve tissue. Plural: ganglia. 



The Insects include that division of the Arthropods which have 

 head, thorax, and abdomen separate, one pair of antennae, three 

 pairs of legs, usually two pairs of wings, and which breathe by 

 means of tubes called tracheae. This group includes more species 

 than all the other living animals together, there being about 300,000 

 kinds known already. Experts regard this as not more than one- 

 fifth of all in existence. Not only are there many kinds of insects, 

 but each kind produces myriads of individuals like the locusts and 

 mayflies, whose swarms darken the sky. Their struggle for ex- 

 istence is very severe and this results in manifold adaptations of 

 structure. 



High Specialization. Highly specialized mouth parts for dif- 

 ferent kinds of food, wonderful leg and wing development for 

 swift locomotion, marvelous instincts and complicated internal 

 structure are some of the lines along which insects have developed 

 in order to survive among their countless competitors in the race 

 of life. Some are adapted for aquatic life, some take refuge by 

 burrowing, some live in colonies like bees and ants, others fight 

 their battles alone; some have become swift in running, leaping, 

 or flight, while, others have fallen back on parasitic laziness. 



