Common Insects — Grasshopper and Honeybee 397 



Respiration. — The thorax is divided into three segments (anterior, 

 prothorax; middle, mesothorax; posterior, metathorax) . Ten pairs of 

 external openings or spiracles (spi' ra kel) (L. spiraculum, air -hole) 

 open into the tracheal (respiratory) system on either side of the meso- 

 thorax and metathorax. The spiracles permit the entrance of oxygen 

 and the exit of carbon dioxide. The tubular tracheae ramify to all parts 

 of the body and may have enlargements called air sacs. The blood does 

 not play an important role in respiration (Fig. 194) . 



Excretion and Egestion. — The coiled Malpighian tubules in the 

 hemocoel collect wastes and empty them into the large intestine. Solid 

 materials are eliminated through the anus. 



Fig. 194. — Photomicrograph of a portion of grasshopper trachea with its 

 branching tubules, both large and small. The tracheal rings and nuclei are quite 

 distinct. (Copyright by General Biological Supply House, Inc., Chicago.) 



Coordination and Sensor^^ Equipment. — A dorsal brain (three pairs 

 of ganglia) is connected by a pair of circumesophageal connectives with 

 a subesophageal ganglion. The ventral nerve cord continues posteriorly, 

 with a pair of large ganglia in each thoracic segment and five pairs of 

 ganglia in the abdomen. A sympathetic nervous system supplies the 

 spiracles, muscles of the digestive system, etc. 



The compound eyes are covered with a cuticular cornea (L. corneus, 

 horny) divided into numerous hexagonal facets (L. facies^ face). Each 

 facet is the external surface of a unit called an ommatidium (om a -tid'- 

 ium) (Gr. ommation, little eye; idion, diminutive). Each ommatidium 



