172 GENERAL ZOOLOGY 



The nervous system generally consists of a "brain," 

 dorsal to the gullet, two connectives passing one on either 

 side of the gullet and uniting below to form a ganglion, 

 from which a double nerve cord extends along the ventral 

 body wall to the posterior end. Sense organs characteristic 

 of the phylum are jointed antennae, and simple and com- 

 pound eyes. 



From the foregoing statements we come to recognize a 

 few features as distinctive for all arthropods. These dis- 

 tinguishing characteristics are a segmented body covered 

 with a chitinous exoskeleton and with jointed appendages 

 arranged in pairs. 



