25 



aparrow and the Iriflh snipe) the colours are darkened. The 

 second is caused by defect in the quality of the colouring-matter 

 of the feathers, rendering them pale, and in some cases almost 

 mouldy looking. In the third group, either single feathers or 

 the whole plumage become a bright white. Beautiful examples 

 ■of the last two groups were exhibited by the kindness of Mr. 

 Pratt. 



These broad lines of variation are found to apply equally to 

 •other branches of living creatures, butterflies and moths (lepi- 

 doptera) being especially instanced ; and it was observed that 

 •experiments on lepidoptera were now being carried on by various 

 persons with the object of learning the composition and modifica- 

 tion of the colouring -matters, the manner in which the colour of 

 insects is modified in nature, and other questions relating to 

 variation, that group of insects affording considerable facilities 

 for the purpose. Our own member, Mr. Merrifield, being one of 

 the pioneers in such investigations. 



The lecturer concluded by stating that he had as far as 

 possible confined his remarks that evening to facts, reserving 

 the theories founded on them for another occasion. 



WEDNESDAY, MARCH 14th. 



CERTAIN DEVELOPMENT THEORIES 

 ILLUSTRATED BY VARIATION IN 

 THE PLUMAGE OF BIRDS, 



BY 



MR ARTHUR F. GRIFFITH, M.A. 



Mr. Grifiith pointed out how strongly variation in the 

 plumage of birds suppoi'ted the theory of evolution, but referred 

 to the great diflaculty in the way of the acceptance of Darwin's 

 or any other existing theory as a complete account of the method 

 in which evolution works. This difficulty he stated as follows : 

 That the struggle for existence should perpetuate an advantageous 

 variation requires that one individual of one sex with an 

 advantage over its fellows and no countervailing disadvantage 



