Vol. XXXV.] 72 



animals, are plastic creatures and their evolutionary- 

 standard is not solely to be determined, by external 

 features. On the contrary, every single organ has its 

 own tendency to develop along definite lines, and once 

 started it will go on developing until, and unless, checked 

 by natural selection. Hence in one group you will have 

 a tendency to increase this or that external feature, and 

 in another the development o£ peculiarities of colour. 

 What we may call a physiological "diathesis" will in 

 one group favour the development of the blood-pigments, 

 and in another of the lipochrome or fat-pigments, and so 

 on; hence we get red, yellow, or green types. Not merely 

 colour, but pattern varies in the same way. Thus it is 

 that in some groups you will find coloration will be no sort 

 of guide whatever. 



An illustration of the pitfalls to which the use of 

 coloration alone will lead, is furnished by the Ducks, which 

 on this factor are divided into a number of genera, obviously^ 

 furnished on the characters of the males. If, instead, the" 

 females had been used, the number of genera would have 

 been very materially reduced. 



A little time ago I had occasion to write part of a book 

 on British birds, and I had to write hurriedly. As a con- 

 sequence, in the concluding chapters, wherein I summed; 

 up my remarks on classification, I find I did not express | 

 myself at sufficient length to carry exactly the meaning) 

 I had intended to convey. I stated tliere that it wasj 

 impossible, without juggling with facts, to recognise the] 

 genus u3£(/ialitis, which should be included in the genus] 

 Charadrius, and, further, that colour was a factor which] 

 must be ignored when forming genera, if classification wasi 

 to be framed on sound, scientific, lines. I began forming! 

 my genera on the more deep-seated characters and not oni 

 coloration, which, for the purpose, I found to be useless.] 

 Turning recently to the ' List of British Birds ' bj 

 Dr. Hartert and Mr. Witherby, I found that the genus 

 ^gialitis had been disallowed by- them ; and turning agaii 

 to the Finches, and to quite a number of other groupsj 



