viii PREFACE 



F. B. Paddock, J. B. Bagley, and W. H. Thomas for reading 

 the manuscript for certain chapters. Drawings for several 

 of the illustrations have been made by G. A. Geist and 

 W. J. Skeeler. Credit is given for each illustration, not 

 original, in the list of illustrations. 



J. 0. MORGAN. 



COLLEGE STATION, TEXAS, 

 Nov. 1, 1916. 



