vi PREFACE TO THE FOURTH EDITION 



It is still a pleasure to acknowledge the cordial cooperation 

 among other members of the zoological staff in such sug- 

 gestions as their several experiences and observations have 

 prompted. Should others who use the book feel disposed to 

 offer suggestions touching either the matter or the method 

 of the manual they may be assured of the cordial thanks of 

 the authors. 



C. W. H. 



G. T. H. 



SYBACUSE, 1922 



