190 MESSRS. ROBINSON AND KLOSS ON 



main b\'' a method of trial and error, and variations which prove to 

 be better adapted than others to the environment become dominant 

 in tliat environment ; it does not necessarily follow that that varia- 

 tion which is dominant in one locality, and has, therefore, acquired 

 subspecific distinction, may not more or less frequently occur in 

 other localities and environment where, however, it is more or less 

 rapidly suppressed. 



Incidentally it may be remarked that Mr. Baker, as evidenced 

 by his work on the Dicruridae, and on the woodpeckers as noted 

 above, is a great believer in average. His average is merely the 

 arithmetic mean and, therefore, assumes that his curve of variability 

 is symmetrical in all cases, which is extremely improbable. It 

 would be far better if he would plot his dimensions and give us the 

 median. In the particular case of this woodpecker, he can be safely 

 challenged to plot the lengths on a base line of latitude and then 

 state that increase of wing-length is not definitely associated with 

 increase of latitude. It is probable, of course, that another factor 

 may tend to obscure the result, as birds inhabiting higher altitudes 

 are usually larger than those from near sea-level. 



In regard to our present series, four birds have had exact data 

 recorded, all fr<3m the immediate vicinity of Koh Lak. Their wing 

 measurements are 140, 139, 135, 136 mm., while one from Bandon 

 measures 135 mm. 



Nineteen birds from various localities from the Pakchan 

 Estuary to North Johore range from 122-133 mm. in length of wing, 

 five being 130 or over : of these five, four are from altitudes of 2000 

 feet and over, while of the remaining fourteen, four only are from 

 the hills. Four birds from Borneo measure 120-123 mm. ((7. m. dayah 

 Stresemann). 



Eleven birds from Sumatra measure 116-132 mm., of which 

 one only is over 130, while that with a wing of 116 is worn. 



A. Hume Ac Davison, Stray Feathers, vi, 1878. E- O. Grant, Fasciculi Malayenses, iii (BirdsK 1905. 



B. Muller, Die Ornis der Insol Salanga, 1882. F. Kobinson and Kloss, Ibis, 1910-11. 



C Gates, Birds Brit. Burmah. Vols, i & ii, 1883. C. Gairdner, .Tourn. N. H. Soc. Siam. i, 191"). 



D. Bonhoto, P. Z. S. 1901. Vol. i. H. Robinson, Journ. F. M. S. Museums, v, 191.'> 



JOURN. NAT. HIST. SOC. SIAM. 



