VI PREFACE 



suited but none followed consistently. In the interest of the 



beginner simpHcity is desirable and to this end a number of 



unimportant, obscure or aberrant groups have been omitted 



and only three grades, or orders of groups, recognized, viz., 



Branch or Phylum, Class, and Order. The classification of 



animals given in the 'Xehrbuch" of Claus-Grobben has been 



followed more closely than that of any other author. 



Acknowledgment is due the publishers, Messrs. P. Blakis- 



ton's Son & Co., for the loan of many figures from the works 



of Galloway, Stevens, Folsom and others. The Macmillan Co. 



and Henry Holt and Co. have also kindly furnished several 



figures. More specific acknowledgment is made in connection 



with each borrowed figure. 



J. I. Hamaker. 

 College Park, Va. 



