ACKNOWLEDGEMENTS 



I wish to acknowledge my great obligation to Miss Mary V. 

 Thayer for her careful and artistic work in the preparation of the 

 drawings. By an oversight, Miss Thayer's initials were omitted 

 from a few of the cuts. She made all the drawings to illustrate 

 the text. I am also greatly indebted to Mr. Paul R. Jenks, and 

 to Dr. Marshall A. Howe of Columbia University, for reading 

 the proof and for assistance in determining the pronunciation of 

 the scientific names. 



