168 BRITISH APHIDES. 



which last hue in reahty partakes more or less of in- 

 tense violet or purple. 



In many cases these colours appear to depend on the 

 differing conditions of the vitality of the insect, for it 

 is to be noticed that as autumn approaches and cold 

 weather reduces the activity of Aphides, the lively 

 greens and yellows commonly become converted into 

 ferruginous red, and even dark brown. 



These changes have some analogy with the brilliant 

 hues assumed by the maple and other leaves during the 

 process of slow decay, and the changes effected in 

 chlorophyl by different degrees of oxydation. Chloro- 

 phyl, thus acted on, successively passes into Erythro- 

 phyl, Xanthophyl, and finally into the dense black which 

 in leaves is the mark of death. 



This view would appear, indeed, in some cases to pass 

 beyond a mere analogy, for Schultz has shown that 

 chlorophyl is the chief colouring matter in Volvox, 

 and in certain low forms of animal aquatic life, such 

 as Hydra, Stentor, and Ophrydius. 



An easy method of obtaining chlorophyl consists in 

 digesting crushed green holly leaves in hot alcohol, and 

 then agitating the cold strained solution with carbonic 

 disulphide. This liquid falls to the bottom of the 

 infusion, after having abstracted the greater part of the 

 chlorophyl. 



Prof. Filhol* has shown that an acetic acid solution 

 of chlorophyl produces with a copper or zinc acetate 

 a fine green colour, and advantage is taken of this by 

 some manufacturers to enliven the colour of their 

 pickles, much, however, to the detriment of the con- 

 sumers of their articles of provision. 



Keeping in mind the above jDroperties of chlorophyl, 

 the following experiments were made, to learn how far 

 the colours of Aphides followed the deportment of the 

 colours of leaves under similar treatment. 



Separate aqueous solutions were prepared both of the 

 dark-brown and the yellow-green varieties of Aphides. 



* 'Extr. Journal Chem. Society,' vol. ii, 112, 1876. 



