December 



207 



mussel shell shows 



that they are true 



scale insects. As long 



ago as the year 1518 



a kind of scale was 



observed upon cactus 



plants in Mexico 



( Cossus cacti ). It was 



found to contain a 



red colouring matter, 



which forms the basis 



of the rich carmine 



used by water-colour 



painters, and it also 



yields the cochineal of commerce, so much employed 



m dyeing and in various arts. 



COCHINEAL INSECT ON CACTUS. 



APPLE MUSSEL SCALE 

 (Much magnified). 



y/^ /"^^-?^^> 



f * . 



An Indian scale insect (Cossus lacca) deposits a 

 ish waxy substance upon the twigs and branches 



