74 ELEMENTARY ZOOLOGY 



spiders and centipedes and crabs and crayfishes which 

 have the body composed of a series of segments or rings 

 and have legs or appendages each composed of a series 

 of joints or segments make up the branch Arthropoda. 

 And so might be enumerated all the great branches or 

 principal groups into which the animal kingdom is divided. 

 In the remainder of this book the classification of 

 animals is always kept in sight, and the student will see 

 the terms species, genus, family, order, etc., practically 

 used. In it all should be kept constantly in mind the 

 significance of classification, that is, the existence of actual 

 relationships among animals through descent. 



