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working through a large collection of desert insects, and that 

 he could thoroughly endorse Col. Yerbury's observation that 

 cxxiv] 



the Desert Region extends from W. Africa to India. He 

 also remarked that the Egyptian flora was dependent on 

 the Nile, and had consequently wandered out of its proper 

 region. This would partly account for the presence of. a 

 desert fauna so far up the Nile as Dr. Longstaff had found it. 



Several other Fellows also gave instances of species which 

 had been found at widely different points of this extensive 

 desert range. 



Dr. F. A. Dixey remarked that a second species of Papilio 

 had been taken on the White Nile. 



Mr. G. A. K. Marshall observed with regard to the great 

 number of specimens of Teracolus in comparison with the 

 scarcity of individuals of other groups, that wherever this 

 genus was abundant, even in other than desert areas, he had 

 always found that there was very little else in the way of 

 Rhopalocera. 



cxxx] Wednesday, December 4th, 1912. 



Metallic Colour in Chrysids. — Dr. G. B. Longstaff 

 exhibited a small box of Chrysids, and started an interesting 

 discussion on the means by which the metallic coloration was 

 produced, observing that coloration of this kind was probably 

 always due to structure and not to pigment. 



Prof. Poulton remarked that this metallic coloration in the 

 Chrysids was always situated in chitin, that it was more 

 probable that it was produced by thin plates than by fine 

 lines, but might possibly be due to interference of light by 

 extremely minute particles. 



The President said that there were many more Hymeno- 

 ptera besides the Chrysids which displayed metallic colouring; 

 he had made many experiments on the subject and found that 

 by transmitted light the actual colouring was, in all cases 

 that had come under his notice, of a testaceous red, without 

 any metallic appearance. 



