PHYLUM ARTHROPODA. INSECTS 



237 



Air sac Thoracic spiracle Dorsal tracheal trunk Eighth abdominal spiracle 



■Lateral tracheal trunk 

 ^Ventral tracheal trunk 



Thoracic spiracle First abdominal spiracle Air sac 



A 

 Cell membrane Tracheole on muscle fiber 



jm 



Figure 137. A, diagram of the tracheae in the body of a grasshopper. The tracheal system 

 consists of air-filled tubes which branch into others. The arrows indicate that the grasshopper 

 inhales through spiracles located in the anterior part of the body and exhales through those 

 limited to its abdomen. B, a large tracheal trunk and some of its branches. (A redrawn from 

 College Entomology, by E.O. Essig. Copyright 1942 by The Macmillan Company.) 



tern is localized in the mitochondria of the 

 cell. 



Excretory system 



The organs of excretion (Fig. 136) are 

 the Malpighian tubules that are coiled 

 about in the hemocoel and open into the 

 anterior end of the hindgut. These tubules 

 remove metabolic wastes; for example, uric 

 acid is taken from the blood that fills the 

 hemocoel, condensed in the tubules to crys- 

 tals and discharged into the hindgut for 

 evacuation through the anus. The conserva- 

 tion of water in this process results from its 

 reabsorption through the tubules. The re- 

 moval of wastes in the dry state is charac- 

 teristic of small land animals that have only 

 a limited water supply. 



Nervous system 



The nervous system (Fig. 138) includes a 

 brain (supraesophageal ganglion), dorsally 



located in the head, consisting of three pairs 

 of ganglia fused together. These ganglia 

 supply the eyes, antennae, and other head 

 organs. The brain joins, by two connectives 

 around the esophagus, to the subesophageal 

 ganglion. This ganglion consists of the three 

 anterior pairs of ganglia of the ventral ner\'e 

 chain fused together and supplies the mouth 

 parts. The ventral nerve chain continues 

 with a pair of large ganglia in each thoracic 

 segment. The ganglia in the metathoracic 

 segment are particularly large and represent 

 the ganglia of this segment and of the first 

 abdominal segment fused. Five pairs of 

 ganglia are present in the abdomen. The pair 

 in the second abdominal segment comprises 

 the pairs from the second and third abdom- 

 inal segments fused together, and the pair 

 in the seventh segment represents the 

 ganglia of the seventh to the eleventh seg- 

 ments combined. Connected with the brain 

 are ganglia of the so-called sympathetic 



