PREFACE. 11 



Although the table of contents had not been prepared, the possible scope of 

 the volume and the order of the topics had often been considered. It was the 

 intention not only to read each other's chapters, but to discuss and revise them 

 together. With characteristic generosity, Professor Mall suggested that, except 

 for one chapter not contributed by either one of us (Chapter VI), we share equally 

 in that part of the undertaking not included in the special studies. Partly in 

 accordance with this desire, he wrote the introductory chapters in the first person 

 plural, much against my earnest remonstrance, for my share in them is quite 

 negligible. However, since they had been considered together they stand as he 

 wrote them, except for a few footnotes. Unfortunately, only one of my studies 

 was in final form before his death, but he was familiar with it, although we had 

 not considered the paper together. Since all the remainder of my part was written 

 subsequently, it did not seem justifiable to me to charge him with responsibility 

 for conclusions of my own or for personal opinions which might not have com- 

 mended themselves to him. 



It is with the greatest satisfaction that I record in this connection his decision 

 to mutually consider all points of difference and, if common ground could not be 

 found, to state frankly our individual views. It was characteristic of him never 

 to use the weight of his authority in the discussion of controverted questions or 

 to influence anyone's conclusions. He was ever willing to leave the truth to 

 the future. It was this attitude that made the completion of this unfinished 

 work a very satisfying effort, even if lonely and in some respects unsatisfactory. 

 Chapters I, II, and VIII, and all the protocols at the end of Chapter IV, below 

 No. 1,000, fortunately had been written by him. However, in accordance with his 

 intentions, protocols were revised and a number of them entirely rewritten. Since 

 he himself had requested this in the case of several which we considered together, 

 I feel that I have merely followed his desire in this matter. In the exercise of this 

 privilege and duty of revision I have used the greatest care to preserve his descrip- 

 tions as far as possible. Indeed, in the completion of this volume, it has been my 

 constant purpose to follow his plan, to preserve his views, and to realize his in- 

 tentions. Although I feel the deepest scientific interest in this work, it has also 

 been a labor of love and devotion, and it was a great satisfaction that its continua- 

 tion was made possible by the Carnegie Institution of Washington, and that its 

 realization was furthered in every way by my friend and former colleague, Dr. 

 George L. Streeter. 



Since these studies were completed very largely during 1918 and the spring 

 of 1919, no references are made to the recent literature in a large portion of the 

 volume. 



A. W. MEYER. 







