CLASSES OF ARTHROPODA. 



77 



Make a table of differences between the grasshop- 

 per, spider, centipede, and crawfish, after the follow- 

 ing plan : — 



Grasshopper 

 Spider 

 Centipede 

 Crawfish 



Make a table of resemblances among the grass- 

 hopper, spider, centipede, and crawfish, according to 

 the following plan : — 



all have exoskeletons 



jointed appendages 



white blood 



reproduce by eggs 



jaws move sideways 



composed, of body segments 



double nerve cord and ganglia 

 Compare this table with the table on page 55. 

 Have any new resemblances been discovered? Have 

 any resemblances on page 55 been omitted? Look 

 for omitted resemblances in your table of differ- 

 ences. 



The grasshopper, spider, centipede, and crawfish 

 represent four classes of animals that resemble each 

 other in the particulars indicated in the table. They 

 are grouped together, and the group is called a Branch. 

 The name of the branch to which these animals be- 

 long is Arthropoda. It is named from the jointed 

 appendages. 



