THE POPULAR INSECT PLAN 



201 



segments and has three pairs of jointed thoracic legs. These charac- 

 ters distinguish any insect. If you will refer to the "Roll Call" 

 you will see that the various orders of insects are distinguished by still 

 other characters, such as the presence or absence of different kinds of 

 wings, or differences in the structure of the mouth parts, which may be 

 modified for various purposes. All insects breathe through tracheal 

 tubes and have a body 



.^./Vclypeus 



upper Up 



mandibla 



rTncuciUotry pcdptxs 



hypoph<xrynyc 



palpife 



COL-rdc). 



maxiilcc 



^ TTjcxxilla 



-Subment-um. 



lotbium 



Mouth parts of the locust. 



armor of chitin, a protein 

 substance something like 

 cow's horn. 



Many zoologists like to 

 use a locust or "grass- 

 hopper" as a laboratory 

 type for study. This is 

 because the body parts 

 are easy to see and be- 

 cause it is a form ha^'ing 

 relatively simple mouth 

 parts. It is provided 

 with two pairs of jaws, a 

 forklike pair, the 7?iax- 

 illae, and a pair of hard 

 toothed jaws, the mandi- 

 bles. These parts when 

 not in use are covered by two flaps, the upper and lower lips (labrum 

 and labiujn). Such mouth parts are found in the bee, although some- 

 what modified from the more primitive type seen here. Moreover, 

 the locust is a more typical insect because it has three distinct thoracic 

 segments, known as the pro-, meso-, and metathorax, and it also has 

 a more nearly typical number of abdominal segments, which in most 

 insects is ten or eleven. The bee, although not such a typical insect, 

 shows so many adaptations, and in addition has so complex a social 

 life, that it is selected as a representative of the class Insecta. 



The honey bee {Apis mellifica) forms colonies which include three 

 kinds of individuals ; first, workers, bees with undeveloped female sex 

 organs, which form by far the largest number in the colony ; second, 

 drones, or males ; and third, a queen, or fertile female. An average- 

 sized colony of bees may contain from 35,000 to 50,000 workers, 

 several hundred drones, and one adult queen. In the following 

 description the worker bee is used, unless otherwise specified. 



