Preface xxi* 



To Dr. Christine Essenberg, librarian and member of the 

 scientific staff of the Scripps Institution, I am indebted for 

 help on the index and glossary. 



And finally, what can I say about the part played in tlie 

 creation of this and my other Avorks by her to whom this 

 volume is dedicated? The extent to which her life is involved 

 with mine in these works only we two can know ; but the 

 wording of my dedication indicates something of the char- 

 acter of that involvement. 



