PREFACE. 
In the Preface to Vol. I. I have said all that is necessary about 
the work. 
I have to thank my friends for the ever-ready help they have 
always given me. Proof-sheets were sent to Drs. Richmond, 
Wetmore, and Murphy, in America ; to Dr. Hartert and Mr. A. 
Goodson, of Tring Museum ; and Mr. T. Wells, of the British 
Museum ; Drs. Stresemann and Rensch, of Berlin. Mr. T. Wells 
also prepared the Index. I wish also to thank the authorities of 
the Natural History Museum in South Kensington, and Lord 
Rothschild of Tring Museum, for all the privileges I have 
enjoyed while compiling the 4 Systema. 5 
In the work I have admitted about 5030 forms, of which 
about 2280 are species; about 990 genera, of which 590 are 
monotypic. 
In a work in which about 9500 references have to be 
consulted, many several times, mistakes are bound to occur. 
I hope those who criticize will come under the heading of 
44 Constructive Critics,” so that we do not hear 44 the cracking of 
thorns under a pot ' 5 (Eccles. vii. 6). 
Towards the cost of the production of this Volume the 
following have subscribed, to whom the Committee of the British 
Ornithologists' Union wish to express their thanks :— 
Sir Samuel and Lady Hordern ; Rear-Admiral H. 
Lynes ; Messrs. W. A. Anderson, W. L. Baillieu, A. Ezra, 
C. B. Rickett, J. Delacour, A. W. Mathews, and Drs. 
Casey A. Wood, G. Carmichael Low, and Manson Bahr. 
In Opinions Rendered by the International Commission on 
Zoological Nomenclature (Opinions 98 to 104, Sept. 1928) is 
no. 103, pp. 21—24, where the case of Grus is very ably put 
forward. This I regard as quite beyond the mark, and is one of 
44 special pleading.' 5 
