170 COLOUR IN NATURE chap. 



not infrequently different from the hind, and the 

 type of coloration suggests that seen in butterflies. 



Among the pure pigmental colours brown, red, 

 yellow, and green are common. A brilliant red 

 colour is far from uncommon, and is displayed for 

 example on the surface of the abdomen in Nepa 

 rubra. 



Among the pigments of the Hemiptera we must 

 assign the first place to the carmine of Coccus cacti, 

 not on account of its importance in coloration but 

 because its commercial value has caused it to be 

 somewhat fully investigated. 



Carminic acid occurs in nature in the Coccidae, 

 especially Coccus cacti, and, according to Sorby, also 

 in various species of Aphis. It is a glucoside, yielding 

 a sugar when treated with dilute acid. 



In the case of Coccus cacti the pigment occurs in 

 large amount in the female (26 to 50 per cent of the 

 body weight according to Krukenberg) and in less 

 amount in the male ; to the dried insects at least it 

 gives a dull red-gray colour rather than a pure full 

 red. According to Mayer it occurs in drops near the 

 periphery of the cells of the fatty body, the drops 

 being less numerous in the case of the male. It 

 occurs also in the yolks of the eggs and in the diffuse 

 fatty body in new-hatched larvae. Mayer says ex- 

 pressly that the pigment does not occur in the gut, 

 but in another place he states that it markedly 

 colours the faeces ; the anomaly is, however, nowhere 

 explained. It is possible that the meaning is that 

 the pigment is not found in the anterior part of the 

 gut, but is introduced into it by the Malpighian 

 tubules. 



