COLOUR-PRODUCING INSECTS. 45 



colouring-matter extracted by the water in which, 

 the insects have been killed. 



The wild variety (grana sylvestra} loses by cul- 

 tivation a good deal of its cottony or downy appear- 

 ance, and doubles in size ; it is then known as grana 

 fina. 



Real cochineal is detected by the following cha- 

 racter : it is wrinkled, with parallel furrows across 

 the back of the insect, which are intersected in the 

 middle by a longitudinal furrow. This serves to 

 distinguish the true cochineal from any fictitious pre- 

 paration. Sometimes smooth black grains called 

 " East India cochineal" are mixed with the genuine 

 article, but an experienced eye easily detects the 

 fraud. 



A French naturalist, Thieri de Menonville, ex- 

 posed himself to great dangers for the sake of 

 observing and studying the cultivation of the cochi- 

 neal in Mexico, in order to enrich by its means the 

 colony of St. Domingo. He carried there the two 

 varieties mentioned above, along with the nopals on 

 which they lived. He discovered also the variety 

 sylvestra living upon the Cactus paresxia, at St. 

 Domingo a discovery that was not without value 

 to Bruley and soon set about the rearing of this 

 interesting little insect ; but death cut him short in 

 his experiments, and Bruley continued them with 

 much success. The posthumous work of Thieri was 



