INVERTEBRATE ZOOLOGY 



CHAPTER I 



ARTHROPODA 

 INSECTA 



A HYMENOPTEROUS INSECT. A WASP 



Observe the shape, color, and external anatomy of the animal. 

 It is bilaterally symmetrical, i.e., it has a right and a left side 

 which are alike ; it has a dorsal and a ventral side which are 

 unlike, and also a forward and a hinder end which are unlike, 

 the forward or anterior end being distinguished by the posses- 

 sion of important organs of special sense and the mouth. All 

 of these features are characteristic of rapidly moving animals. 

 Can you explain why ? On the ventral side are the legs, which 

 are also called appendages or extremities. On the dorsal side of 

 the insect are the wings, which are not called extremities, since 

 only those organs receive this designation, speaking strictly, 

 which are paired projections from the lateral or the ventral 

 surface of the body, and are either used for locomotion or are 

 homologous to locomotory organs, i.e., are directly descended 

 from organs which were primarily used for locomotion. Thus, 

 the wings of bats and birds are extremities, although those of 

 insects are not. 



The external surface of the animal is very smooth. This 

 feature is also correlated with rapid motion. Do you know 

 how ? The animal is encased in a hard shell, called the cuticula, 



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