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, 7.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, 7.¢., 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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